Corki functions very similarly like Graves/Ezreal, they all share escapes, 550 range and general safeness to be first picked. He is a "standard" AD that I personally recommend all newer AD players to play, since he has a great laning phase, strong poking, burst and sustained damage, along with a very generous escape.
13AD Primarily for last hitting. 2% Lifesteal since you're passing up the 3% from masteries.
13 Armor/MR to be able to trade well in lane.
I run 23/0/7, 10% Magic Penetration, 10% Armor Penetration and 10% Crit Dmg are all too good to pass up for Corki. Meditation was also a necessary talent to sustain his mana costs. The rest is pretty obvious.
- Fantastic all round summoner, great vs heavy CC teams (not knockups) such as Sion/Taric/Ashe/Amumu. You can't go wrong with Cleanse, since almost every teamcomp has CC in it.
- Also a all round summoner, allows you to make plays and manage situations.
- Ghost is good against bruiser dive comps, such as Irelia/Jarvan/Malphite, if they have multiple bruisers on the enemy team, then Ghost may just win you a late-game fight.
- Ignite is important if you don't have enough damage on your team to kill off a tanky sustain champion such as Swain. Ignite is also particularly good in lane against Soraka, since it gives you great killing potential.
- Exhaust is great against a single diver, if the enemy team has only one Bruiser, then instead of using Ghost to run away, you can Exhaust and just kill him/her.
- Heal is strong in lane and in teamfights vs AoE. I usually I pair up Heal with Ignite on Tristana, to make her a powerhouse during the laning phase.
Level Q to 4 (just enough to 1 shot ranged minions with Q + R) at lv 7.
Then max E for the damage.
Passive: Hextech Shrapnel Shells
Corki's basic attacks deal 10% additional true damage to minions, monsters, and champions.
This passive is awesome. 10% extra damage. TRUE DAMAGE.
Since I run 15 Flat AD now, it makes this even better.
Q: Phosphorus Bomb
Deals 80 / 130 / 180 / 230 / 280 (+50% of ability power) damage to enemies in a target area and reveals that area for 6 seconds. (does not reveal stealth)
Cooldown 8 seconds
Cost 90 / 100 / 110 / 120 / 130 mana
Having a Nuke on a carry is awesome, nukes scale the best during early game... Ex: How strong any lv3 champion is compared to a lv2 champ. Since they removed the 35% Blind (OP AS HELL) and added the Sight on Target, Phos Bomb is at a better place over all. It's still a great nuke to level up first, and doesn't become insanely useless late-game.
Tip: Try and pair up your auto attacks with a Phos Bomb when harassing.
Corki surges to target location dealing 60 / 90 / 120 / 150 / 180 (+40% of ability power) damage per second to enemies in the fire left along his path.
Cooldown 20 / 18 / 16 / 14 / 12seconds
Cost 100 mana
Great escape and engage ability. Can go over ledges/walls. The single downside is it's super high mana cost, so be careful when using it during the laning phase.
E: Gatling Gun
Corki's gatling gun fires at all targets in front of him for 4 seconds, dealing 20 / 32 / 44 / 56 / 68 (+40% of attack damage) physical damage and reducing 1 / 2 / 3 / 4 / 5 armor per second. The armor reduction stacks and lasts 2 seconds.
Cooldown 16 seconds
Cost 60 / 75 / 90 / 105 / 120 mana
-50 Armor at level 5, along with great damage. Great for Dragon and Baron. Gatling Gun was recently buffed, so now it does crazy amounts of damage.
Since the cooldown is pretty long, make sure every Gatling counts, especially during end game fights.
R: Missile Barrage
Corki fires a missile toward his targeted location that will collide with the first enemy it hits. Each missile deals 120/190/260 (+20% of attack damage) (+30% of ability power) area magic damage.
Corki stores one missile every 10 seconds up to 7 missiles at any given time.
Every 4th missile will be a Big One, dealing 50% extra damage.
Cooldown 1.2 seconds
Cost 30/35/40 mana
Your Missile Barrage accuracy is a tell about how veteran of a Corki player you are. Making sure every Missile Barrage lands means a lot in small skirmishes and duels, I often rethink a lost duel that would've easily been won had I landed one or two Missile Barrages.
Great for clearing waves.
Your goal is to farm, and since your auto attacks hit really hard, there should not be an excuse to miss any last hits at all.
Once you hit level 3 and get level 2 Q, you can try to be aggressive, depending on your lane composition and your enemies, this may or may not work. If it doesn't, realize so and continue farming.
Remember that Valk is 100 mana, so only use if you REALLY have to. Phos Bomb also costs a lot of mana, if you want to clear waves, then try to use Missile Barrage.
Tip: At level 7 (With level 4 Q and level 1 R) you can clear an entire ranged minion wave in the back.
Since you're Corki, you are already strong mid game compared to other AD carries(Because you have nukes!). You can either try to force 1v1 situations vs other champions, farm lanes/jungles with your mobility, or teamfight at Dragon. All options are open. Most of the time though, you will end up just farming, but realize that you are likely stronger than most other champions (specifically other AD's) in the game.
Take advantage of your mid game strength!
At this point, your damage should be at its peak. Anything that walks near you should melt. However, the major drawback is your attack range. Kog/Trist/Cait all have a much easier time hitting targets than you will. The most effective way to play MOST teamfights late game is to hit whatever target you can... really really hard. But always be aware of squishies that are overextend, don't be afraid to Valk into them and initiate.
Corki is extremely well rounded. He has decent damage, poke and an escape. You can kite extremely well. I always find myself last hitting extremely well with his attack animation and passive. I recommend Corki as a beginners AD since he is fairly easy to play (all you need to do is auto) but extremely hard to master (positioning with an escape and landing all Missile Barrages).