start with a pile of photos. look for interesting color combinations, textures, details, and other things that make you happy. get a good variety!
use a one inch square punch to cut out a section of the photo.
find a frame for your photos. i like ribba frames from ikea. this one is 9x11.
lay out your one inch photos and play with the rows and columns until you like your arrangement. i tried to make sure that all the colors, themes, and textures were distributed evenly throughout. i think it would look neat arranged by color too. cut a piece of cardstock for your background (i used white) and adhere it to the mat.