I needed to cover a large area of wall where our stairs are, so I decided to put decals up. When I shopped on line for them, I realized it was going to cost a ton of money to do what I wanted to do, so I decided to make them myself.
-vinyl shelf liner
-small "sampler" size cans of latex paint in the colors of your choice
-foam paint brushes (less brush strokes are visible on your finished project)
-something to cut out the shapes (I bought a tool that cuts ellipses)
I cut out a bunch of different sizes, and taped them all down on some newspaper. I'm sure you could use double sided tape, but I just rolled some tape loops. You'll need to put two coats of paint on your decals. Don't try to put too much paint on them or else you'll have major curling problems. Use more tape if you need to, to keep them from curling too much. Also, make sure the first coat is completely dry before you try to do the second coat. You may need to let it dry overnight, up to two days.
After the second coat has dried, peel and stick!