This is a ranked Irelia tutorial. I will explain the best way I know how to play her after much ranked play with her and watching the highest elo players use her (big thanks to bigfatjiji!). This whole build is based on early game dominance. You want to almost exclusively go mid. Second option is solo top. Third option is laning with a support that will let you farm (Sona and Irelia duo works very well). Fourth option is jungle but I seriously suggest that you do NOT do this. This is a total waste of her early game lane dominance and she is much weaker at jungling than other champions such as Warwick, Udyr, Olaf, Amumu, etc.

Anyways, down to the strategy. I play Irelia as a burst assassin anti-carry bruiser tanky dps all-around ownage sonova*****. Your role in teamfights is to kite and take out their squishy carries. Actually, your role in the whole game is to counter their squishy carries. I like to take mid and vs champs such as Karthus, Ashe, Vlad (what?! you can beat Vlad?! - yes, once he pools hes ****ed. til level 9 and gets 3 hextechs of course -_-. nerf that **** plz), basically any ranged dps carry or ap nuke. What counters her early game are champs with steady heals such as Nidalee so try to get solo lanes without champs like that. The idea is that even from level 1, harrass the **** out of your opponent. Constantly Q-E combo them. Your 6 potions will keep you in lane and either zone or FB them and their Doran items lol. A little trick is to use your Q's "passive" to get within range of your opponent. Say he is standing behind his minions and you are standing behind yours. Once one of his minions gets low enough to kill with your Q, Q the minion then Q-E combo him and back off. Almost constantly do this. This strategy will help you build up your farm while preventing theirs. This is why I don't get W until so late. Play Irelia as more burst with your Q-E then autu-attacking with W. Once you hit 6 is where the fun starts. You can be much more reckless with harrassing them as all you have to do is heal up on the minion wave. 4 blades to the wave will take them all out and give you all the last hits except on the big ones.

PROS
great burst all game
skills scale well into late game
short cooldowns on dash and slow/stun
sexy dance
ridiculous cc reduction
mix of physical/magic/true damage= hard to counter

CONS
ugly skins

AP marks- standard for any physical carry

Armor seals and MR glyphs- I really like these runes because it gives that little bit of tankiness early game that helps Irelia to dominate her lane.

HP quints- same as above

21-0-9

Pretty self-explanatory, standard set-up for physical carry. 1 point in 15% increased buff time because buffs are just so so so good on her. Try to take a blue or red whenever they are available.

key sequence: do not be tempted to rush your sheen. the early catalyst is essential for the type of gameplay I'm promoting. Gives you tankiness and a much larger mana pool, both of which you need.

1. start off with rejuvenation bead, 4 hp pots, 2 mana pots
2. try to b when you have enough for catalyst and boots, if not just get ruby crystal and boots then build to catalyst
3. sheen- start with saphire crystal (extra mana is great for the skill spamming you will be doing)
4. phage- tankiness and slow ftw
5. trinity force
6. merc treads- the reason I get boots so late is because in lane she does not need that much mobility because of her Q, rushing your trinity force is much more important. BUT, if the game starts to develop into the teamfight/ roam phase, definitely get merc treads earlier.
7. finish off banshees
8. youmuu's ghostblade- I found this to be a better alternative to Phantom Dancers as it gives extra AD, which stacks onto your Q, and also extra ArP.
9. bloodthirster- this combined with your W passive and R gives you so much survivability. ****
10. guardian angel- so you can do dumb **** and still come out on top.

Ghost- great all around spell

Cleanse- This just makes Irelia awesome. Combined with her passive and merc treads, she can seriously run through the enemy team and neutralize their squishy carry. Also is great for baiting, get stunned, ghost and cleanse and shoot R back into enemy team then Q-W-E in when your team engages

While you will be tanky, you are not a tank so never make the mistake of blindly initiating because you cannot soak enough damage for that. Since I play Irelia as a burst assassin, I usually do not come in right when team fight starts. Try to flank their carries and Q-E in and finish them off. Also, use your E well. A well timed stun can make or break a teamfight. You can also win many fights you normally wouldn't be able to because of the stun.

Cheers