The Artistic Mother workshop. Shona of An Artful Life and author of The Artistic Mother has done a post about this with a tutorial. I really suggest you take a look at it because she goes into detail breaking it down into steps showing how to make and use a view finder in order to help you make the proper combinations. It's a very easy method and can be used on many projects.
I used my background papers from Week One to make these. The first two were made by tearing and cutting up strips of my papers and glueing them onto a playing card. The last photo is a greeting card. The same process was used. The papers were glued onto some card stock that was folded in half to make a card instead of onto a playing card.