Here's a quick and easy craft I did recently. I decorated a B for my little guy's door.
It's really easy, all you'll need is:
-Ribbon/Buttons/Decorations of any kind
-ModPodge & Hot glue
Turn the letter over on the paper and trace the outline.
Then cut around the outline with about a 1/4" allowance
Next put some ModPodge on the paper and lay the letter back on it.
(Not pictured) Wrap the paper around the sides of the letter and glue down with ModPodge. Cut the holes out also leaving some allowance to wrap down the edges.
Once the ModPodge is dry, decorate. I used some ribbon that I had from some baby shower presents that matched the colors I'm going for in his room. :-D Don't you just love to reuse free stuff? lol
Here is how it turned out...
To hang I just used a staple gun to staple it to the top of the door.