what I did was sit at my kitchen table and peruse all of my collage mags (old martha stewerts, O magazine, and a few various mags I found at goodwill etc) I start with a color in mind...then I cut out texture, colors, objects and other bits that complement my inspiration.....
when I was ready to collage, my entire dining room table was covered with different pictures. I had three groups....green, red and aqua. from those three, I picked and chose pieces to complete each "sqaure".
I realized a few things:
*take the time to cut out your pictures when you find them (instead of "roughly" cutting out pics and then figuring that you will cut the excess out later)
*having larger pieces of color and texture are important for a background or base
*trying things that seem like they don't fit is a good way to find neato combos.
*sharp scissors are a must
*glue stick is damn sticky
*card stock is great to have on hand...the more colors the better
*scrap book papers are really cool too, especially vellums and textured paper
saving all your bits when you are done is a good idea...I put mine in an envelope until I am ready to collage again.