Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Summer Spells: Exhaust/Ghost
Reasons: Exhaust for 1v1 or getting those extra getaway kills.
Ghost for getting away or catching up to the battle.
Runes: Armor Pentetration, Crit Damage, Crit Strike, Health
Items: Hexdrinker, Berserker Greaves, Last Whisper, Infinity's Edge, Phantom Dancer,
Phantom Dancer, Black Cleaver (replace Hexdrinker), Phantom Dancer (replace LW)
Early Game: Be a bit defence because your attack speed isn't high enough to attack enemy's from your Hiten Style. When you get berserker greave's start getting aggresive, but not too aggresive. Irelia is a squishy champ so just because your ulti has an op heal don't fly into the battle like a tank. USE YOUR ULTI WILLINGLY! Your ulti has such a low cd use it to gain health from big creep waves.
Mid Game: This is were your assasin part comes into play, you are an awesome tank/squishy killer so gank alot. Beware of tough champs though, Jax for example. Use your ulti in team fights were it is very affective then rush in for kills with your e/q.
Late Game: Now your deadly should having Infinity's Edge. Snag red/blue buff to become even more. REMEMBER! Even though you are deadly you are still squishy you still arn't a tank!
Kill Rotation: W, Q, E, R, E, Q -> W, E, Q. Should be dead by now.
Hope this helped, have fun with Irelia!!