any tips for completing an alley-oop?

i can get the tosses going on the keyboard ie. the backboard, big screen. But i cant complete the alley-oop. Any tips? When to jump....what to press???

Cheers.

Just keep practicing
That is the best way to master it, everyone has had to practice alot

Try running the quickplay "basket cut" then try the alley-oop.

Oh, do you mean in Dunk Competition or In-Game?
You can't go off the Jumbotron or Backboard In-Game so I assume you mean Dunk Competition