For the record, I did not hang these by just eyeing them. Here's an easy way I've learned from some bloggers for figuring out how you want to hang a collage of pictures on a blank wall without making multiple nail holes.
1. lay the frames on the floor or a table and shuffle them around until you like the layout.
2. take a paper bag and trace over your frames so that you can cut out their shapes
3. using painter's tape (other tape may peel your paint!), stick the cutouts onto your wall in the same way you laid out your frames, moving them a little here and there until it looks right.
4. at this point, you can either figure out where the nailheads will need to go, or do like I did and use the Command hanging strips (we have plaster walls, so I try to avoid using nails).
5. hang the pictures and admire your work!