How do you use irelia ult correctly?

There is no cast time so you can use it while running away and during AA animations.

I use it to either prep minions for Q resets (like to jump on a gnar) Or to ready sheen procs while fighting.

The heal is kinda meh, but it is an option to survive something you otherwise wouldn't have (Shoot it through a minion wave and the enemy champ at the same time and it can heal an okay amount)

But yeah...mostly minion prepping for Q jumps or just for weaving between auto's for sheen