I use sketches a lot when I'm doing layouts as a way to inspire me and to give me a starting point. I don't always follow the sketch exactly and may even end up with a layout that looks completely different. A lot of times a sketch will call for using one or two pictures but I want to incorporate more on the layout. This is when I will decide to do a PICTURE COLLAGE of some sort. I define a collage as anything where the pictures are grouped together. This can be done by hand while you are arranging your layout or done digitally in several different programs. For those of you who use Photoshop, I'm sure you may already know how to do this. If not, there are great tutorials out there to show you how, such as this one by Photoshop Online Tutorials. There are also some great programs that are free such as Picasa. Here is a youtube tutorial for collaging in Picasa.
I have done collages digitally before (such as this one), but I really enjoy just trimming my pictures to make them work for me. Here are a few examples: