A big part of a successful WILD depends on how tired you are. Too tired and you fall back asleep, too awake and you lie there forever and get frustrated. With practice you'll discover the conditions that suit you best.

The other hard part is knowing how/when to "jump in" the dream. You need to wait until it's like you're watching a movie (sometimes you're hearing it too,) then you enter the dream. That part is hard to explain but you'll know it when you do it. Good luck.

EDIT: Oh, and do a search on dream re-entry. There was a good post about it a while back (it may even be a tutorial.)