When I first tried to do a collage (I did some sort of scrapbooking on a frame with canvas on), I used glue. And I mean regular liquid glue. That wasn't a very good idea. The paper easily got bubbly and I had to put it underneath a stack of books not to dry bubbly as well.

Then I got a tip from my friend: Photo mounting squares. I LOVE them! It's SO easy, it sticks well and it doesn't need dry-time. Probably all of you guys already know this, but if someone hasn't tried them, I really recommend them. Also, Glue Dots are great adhesives and come in various sizes but are generally a little thicker than the mounting squares.