I purchased some decals for the nursery a few months ago.
They took a little while to get here, and once they did (surprise, surprise) I was indecisive as to where they should go. One day I just put them up.
The giraffe is on the wall as you walk in:
And the birds (an extra one on account of the delay in the seller getting them out) are on a mirror that will eventually go above the crib. No, the nursery isn't completely complete yet, but it's ok-she's still sleeping in our room for a little while longer. Also, I thought the birds were a little girly if it were a boy, so I didn't want to commit to tacking the mirror up if it was a boy. And since we've found out it was a girl, well, we've been busy.
Anyway, the process was super easy and kind of fun actually. Just decide on your placement, rub, peel, tape, rub and peel again. Presto!