I've done a bit of decoupage in the past. It's fun and makes unique gifts.
I'm not too sure about the wood. I typically do glass or plastic. I do know some friends have done wooden stools in the past, though, so I would say stained/finished wood would be ok.
Pictures are fine. I'm not too sure about things printed on white paper. I'm not sure if they would run or not when you put the decoupage on them.
Basically the only hints I have are practice on something small first to see the right amount to use. Don't use too much or too little.
Good luck
