Our photoclub had a workshop on the weekend, and I had a great time learning and building photo collages!
Here are the collages I created during the session:
The trick is making an effective border so the images pop off the background. These were done using a large paintbrush tool, and then going around each photo so only the edge of the brush affected the photo. Also the background is usually made from a photo in the theme you have selected - do the colours are similar - and then the photo is blurred to create a background. I dound it was also effective to choose the photo, and invert it. This way you get colours which are literally complementary to the colours in the photos you have selected (like in the haircut photo collage).
I will be building more, I am sure!