I've noticed a huge difference when I describe rather than praise. I think it makes my kids more confident because they know the criteria. "Good job" is so vague. Description is very specific, and it makes more sense to kids.
I use description with encouragement when they need a little support. I might say, "You picked up all of your dress-up clothes, and put your books back on the shelf, now put the laundry in the chute and the dolls in the crib and you will have a very clean room!" I also adore the How to Talk books.
That's my two cents.
-Jo