Ammo

This is complicated stuff. Find what NPCs resist hole is. I usually recommend people shoot EM into shield based ships, Explosive into armor based ships (depending on race), and Thermal for the off hole in most ships. Drones, use the faster ones, light thermal drones rarely work. I recommend Warriors or Acolytes for light drones, though ec-300's work great for driving off tackle. Use the damages above. And when in doubt, bring friends. Or ask more senior people what ammo to load.

And note, range matters more than damage type.

Ammo matters!

Your choice in ammo changes your damage and range and tracking a LOT. It's important to pick the right type of ammo for the task you're trying to complete. You train T2 weapons because they are almost ALWAYS better at a few tasks, and pretty damn crucial for some fits.

Generally, you should base your ammo amounts on how many reloads you include. You need four kinds: long range pvp, mid range pvp, short range pvp, and a bashing ammo. Most tend to be faction, with t2 where possible. It is small so you can pack a lot.

It is like 5 reloads or so for most pvp groups, and like 20-40 reloads for bashing ammo. This is the cheap t1 stuff used by the super large alliances. You also use this if you're a brand new newbie and struggling.

Ranges are everything eve, and you can EASILY sort what is short and long range ammo by right click on your weapon. At the bottom is your shortest range ammo, while at the top is your longest range ammo. Note that Projectile weapon mid range ammo has tracking speed advantages as well, so take advantage of it. Most times in fleets, your FC will tell you ammo type.

T2 ammo is way better in a few ways. It will have a long range version that does less damage than short range, but more damage than other long range t1 ammo. This varies a lot between weapon systems, especially for tracking. Spike for railguns is very good for instance, while Javelin torpedos are trash. Short range version does massive damage with super short range. Same thing it varies, Void for blasters, while Hail for projectiles is too short.

And T2 ammo is VERY cheap. Like double the cost of t1, and 1/6th of faction. 2000 rounds of the following ammos:

CN Iridium - 1.5 mil (CN == Caldari Navy aka faction ammo)

CN Thorium - 1.3 mil

CN Antimatter - 1.3 mil

CN Iron - 1.3 Mil

Spike - 232k

T1 Antimatter - 153k

Most importantly, practice. Learn your ranges. Know how long it takes to change ammo. With harbingers, the lasers switch instantly, ALWAYS be checking ranges. And know when you need to restock. Realize you can save your fit, and do 'multifit' to restock your ship easily.

Gleam is the short range one, I have Aurora loaded (the long range one), and there are options to load in between ammos as well!

Thanks to @Isaiha Rock for this idea!

Ammo selection

https://imgur.io/a/KSxbcAJ has a full chart of all your ammo choices and what it's good at.

I'll give some advice on ammo selection for new players here, based on their chosen weapon systems.

Note, faction will ALWAYS be better, but way more expensive, like 10x as much.

I have bolded the TWO ammos you should always load if you're T2 fit.

Hybrid Long Range - Railguns - Load Hybrid Charges

These guns track amazing, have a solid alpha, but have limited ammo selections. Damage type locked Kin/therm.

Antimatter - the low range, high damage ammo of your dreams
Iridium - A good mid range ammo, good damage at good range.
Iron - The longest range ammo, but not super useful most times.
T2 Spike - Extreme long range, great damage, maybe the most popular for T2 railguns.
T2 Javelin - Extreme low range, okay damage, I find faction Antimatter to be stronger most times.

Hybrid Short Range - Blasters - Load Hybrid Charges

These are the kings of damage on target at point blank. Damage type locked Kin/therm.

Antimatter - the low range, high damage ammo of your dreams
There's not a good longer range blaster ammo unfortunately, iridum maybe.
T2 Null - GREAT long range, good damage, is often overlooked how strong it is because...
T2 Void - TINY range, HUGE damage, the best ammo upgrade you can do for these guns!

Projectile Long Range - Artillery - Load Projectile Ammo

The king of high alpha TIDI combat. Terrible tracking, but huge Alpha Strike with coordinated hits. You need the most variety of ammo here. All damage types.

EMP - Low range, high damage. Does EM mostly, so great against most shield based tanks.
Fusion - Same low range, High damage. Does explosive, so great against armor based tanks.
Depleted Uranium - A mid range ammo, with mid damage, spread though. Has a BIG tracking bonus
Proton - Long range, low damage, not a huge fan.
T2 Tremor - HIGH range, okay damage, great for alpha strike at range.
T2 Quake - TINY range, great damage, like EMP damage, but much shorter range, not super used honestly.

Projectile Short Range - Autocannons - Load Projectile Ammo

The king of short range pvp with damage switching, great tracking and shoot in fall off more! All damage types.

EMP - Low range, high damage. duh. :D Because you're mostly going after shield ships.
Fusion - Same low range, High damage, just incase they're uber em tanked.
T2 Barrage - Great range, okay damage, great for driving off small things.
T2 Hail - SUPER lower range, great high damage, struggles to track at these ranges though.

Laser Long Range - Beams - Load Frequency Crystals

Need to bash something, these are GREAT. Hold at extreme range, do damage, don't run out of ammo. Optimal range must reach! T1 Crystals do not break but faction and T2 do. Damage Type locked EM/Therm.

Multifrequency - Low range, great damage. The range on these is their downfall, but if they're in range, they do the job 90% of the time.
Standard - Mid range, mid damage. Because you can instant switch crystals, soon as something moves out of range, switch! Note, this has lower cap usage too!
Radio - high range, low damage. Always carry some T1, just in case. T1 non-faction doesn't break!
T2 Aurora - High range, good damage. But it is a red-headed stepchild compared to it's pulse cousin
T2 Gleam - TINY range, great damage. Note that these actually break quick!

Laser Short Range - Pulse - Load Frequency Crystals

Fantastic for deleting a lot of targets in a hurry, instant range switch is huge, great for large fights! T1 Crystals do not break but faction and T2 do. Damage Type locked EM/Therm.

Multifrequency - Low range, great damage. Again, have both Faction and T1, but usually the base for all lasers.
Standard - Mid range, mid damage. Good for standby damage. Note, this has lower cap usage too!
Radio - High range, low damage. meh but just in case.
T2 Conflagration - TINY range, HUGE damage. Note, it has a tracking speed penalty so watch out!
T2 Scorch - Huge range, GREAT damage. Same tracking penalty. These are the best T2 ammos in the game.

Missiles

I'll simplify here.

Match your damage to your ship train bonuses in show info.

After that, match your range/explosion radius to your target.

After that, do the most amount of damage to the target, if your hull is not damage type locked.

Loading Ammo, thanks to Fim Asatru!

Note, how much ammo goes in each turret is dependant on the size of the ammo bay and the ammo itself. This is simple math, but you can also just use this great cheat sheet by our own Hokaba Hanaya. I usually recommend you grab 3 reloads of faction, and 5 reloads of T1 and T2. So if the ammo is 0.0025 m^3 and the bay is 0.3 m^3, it can hold 120 rounds.

You don't have to do this math yourself, you can easily see this from the fitting screen and simulate.

Ammo damage and range

By right clicking on your guns, you can easily see what damage types your ammo offers. In this example, Gleam is your high damage, low range ammo, and does EM and thermal. Radio is your highest range ammo at the top, and only does EM.

Resists and Your Ammo Selection

Some weapons have the flexibility to change their damage types. Thanks to Archondr for giving me the idea of 'why don't just explain super complicated topic instead of writing 10 pages'.

Lasers - only shoot EM and Thermal https://wiki.eveuniversity.org/Turrets has charts and more details.

Hybrids - only shoot Kinetic and Thermal https://wiki.eveuniversity.org/Turrets has charts and more details.

Projectiles - Can shoot all over the board, but has some major competencies! EM, thermal, and explosive all have a short range ammo. https://wiki.eveuniversity.org/Projectile_ammunition has a chart.
Missiles - Can shoot any damage.

You want to shoot into the resist holes of your enemies. This is easy with NPCs, but harder with players. With NPCs, you can do show info on them in space and see their resist holes live. Often, their main damage type is also their resist holes.

https://imgur.com/oRFky7H has a good graph of showing what damage type NPCs do and what they resist the most. It also lists the best 'drones', though some are a little contested in the comments.

For player ships, T1 ships mostly have a resist hole. These resist holes are similar across different races too. The slot layout will dictate if someone will tank in shield or armor. Let's look at a Retriever.

The retriever has a 2/2/3 slot lay out with 3 rig slots.. This would normally mean it's an armor tanker.
But the low slots are usually reserved for mining laser upgrades.
The shield resists are 0/20/40/50, meaning 0% em, 20% thermal, 40% kinetic, 50% explosive. The armor resists are 60/35/25/10%.
The two mids might be reserved for one shield module, and that might be reserved for an active EM hardener. The rigs might be reserved for a thermal and kinetic rig. this brings the shield resists to: 50/44/58/50.
So thermal is most likely the best to shoot into it, as it is the second resist hole for shield, 3rd for armor.

This comes to one bit of advice you could consider: Aim for the second resist hole.

However, people are VERY predictable and they tend to fly similar ships. This is especially true for fleets. So it's very easy to figure out what resist hole they most likely have, and shoot into it.

Why do resist holes matter?

Let's say you are flying a missile ship, and shooting this semi tanked retriever, but they have left off the EM active resistance mod and instead put on a multifrequency shield hardener and damage control. Your missile ship does 100 DPS.

This ship now looks like this from a resist profile: 33k efhp (omni damage), 5,865 raw shields, 39/64/73/70 resist shield profile, 3750 armor hp with 66/45/37/24 profile, and 4800 hull with a 60/60/60/60 profile.

(Note, I'm simplfying heavily here, there is a shield regen rate that can REALLY fuck you, and your missile reloads can also hose you as well. It peaks at 33% so ... yeah. :) I'm going to use the in game average shield regen, which is FAR from accurate.)

EM - Mjolnir missiles - This is your best damage against this ship.
- Your missiles hit 39% shields, hence doing 61% effective damage, meaning you are doing 61 damage per second. The ship has an average passive regen of 13 hp per second, so 48 damage per second effective, so you will break through their shields at around 122 seconds.
- They have 66% armor, so 34 damage per second from your EM missiles, no regen here, so 110 seconds.
- They have 60% hull, for all damage types, so 40 damage per seconds, so 120 seconds.
Thermal - Inferno missiles - Your second resist hole.
- Your missiles hit 64% shields, doing 36 damage per second. Passive regen 13 hp, so 23 damage per second effective, you break through at around 255 seconds.
- They have 45% armor, so 55 damage per second, no regen, so 68 seconds.
- 60% hull, so 120 seconds.
Kinetic - Scourge - Higest resist hole, and one of the most common missiles to be damage bonused, sometimes as much as 25% more.
- Your missiles hit 73% shields, doing 27 damage per second, with a passive regen of 13, so 14 damage per second bleeding through. 418 seconds. That's forever. :D (Note, passive regen will most likely let them tank you forever.)
- Armor at 37%, so 63 damage, 59 seconds.
- 60% hull at 120 seconds.
Explosive - Nova - Third resist hole. Maybe the most under utilized missile.
- Your missiles hit 70% shields, 30 damage raw, minus 13 passive regen, 17 dps bleed thrugh, 345 seconds. Again, passive regen most likely saves this retriever.
- Armor at 24%, so 76 damage, so 49 seconds.
- 60% hull at 120 seconds.

So let's do a summary: EM - 352 seconds. Thermal - 443 seconds. Kinetic - 597 seconds. Explosive - 512 seconds. And Kinetic and Explosive most likely wouldn't have even broken them honestly.

What if they fill the hole?

You do minor changes in their fit though, and holy crap the results are different. Instead of a shield extender, they do a purger and a shield power relay. Their new stats for shields are: 5100 shields, 25 hp/sec passive regen, 56/51/64/57. (Note, this fit is VERY unlikely for a retriever!)

EM - No longer the highest hole. 56% shield resists.
- Your missile hits shields of 56%, you do 44 raw damage, minus 25 hp/sec, for a total of 19 damage effective, smaller shield amount but still 268 seconds to break through. Might even struggle to break through peak recharge with bad reloads.
- Armor the same at 110 seconds
- hull same at 120 seconds.
Thermal - Highest hole now, similar math, but regen still hoses you.
- Your missile hits shields of 51%, so you do 49 raw damage, minus the 25 hp/sec, for a total of 24 effective damage, 212 seconds.
- Armor same at 68 seconds
- hull 120 seconds.

EM takes 498 seconds, Thermal at 400 seconds. Minor change, and you might not even kill the guy if he's over tanked.

What races have what resist holes?

Caldari

Uses Shields, First resist hole is EM, second is thermal.
If armor tanked (VERY unlikely), first and second resist hole is Explosive/kinetic, explosive hole more likely to be filled.

Minmatar

Primarily uses shields, First resist hole is EM, second is Thermal
Can use armor, Primary is explosive, second is Thermal.

Amarr

VERY unlikely to use shield, but primary is EM, secondary is Thermal.
ALMOST ALWAYS armor, primary and secondary is Explosive/Kinetic, but the explosive hole is more likely to be filled.

Gallente

Sometimes shields. Primary is EM, secondary Thermal.
Usually armor. primary is Explosive, second is Kinetic/Thermal.

Short version of using shoot into the secondary hole:

Caldari - Thermal, Minmatar - Thermal, Amarr - Kinetic, Gallente - Thermal

All Weapon System with Short Range ammos

I also made a comparison between a blank canvas sunesis with perfect skills versus itself with all 9 weapon systems you would use on it.

Short range ammo graph:

Light Neutron Blaster II with Void S
150mm Railgun II with Javelin S
Small Focused Beam Laser II with Gleam S
Small Focused Pulse Laser II with Imperial Navy Multifrequency S
280mm Howitzer Artillery II with Quake S
200mm AutoCannon II with Hail S
Rocket Launcher II with Mjolnir Rage Rocket
Light Missile Launcher II with Mjolnir Fury Light Missile
4 Hobgoblin II (Can combine these with other weapon systems on this ship, don't use hobgoblins for pvp though)

And this is the graph that shows what these damage profiles look like, with 2 damage mods on them, no extra tracking etc. target has a 5mn quad, 1 multispec, and 1 damage control. I completed these with Pyfa.

All Weapon System with Long Range ammos