When it comes to hanging pictures on the wall there are a million different opinions on how it should be done. I tend to be an estimator....measure about where you want it, mark it with your finger and hammer in the nail. All the while praying it is really in the right spot.
But when it comes to hanging a collage of pictures, there are a few ways to save yourself a lot of headache. I use 2 different ways, depending on the size of the collage.
For a large collage I lay the pictures out of the floor. I always have rolls of huge paper on hand for the kids to use to their hearts content. I cut a piece of paper the size of each frame. I know it seems tedious but it is much easier that trying to position and reposition nails and frames all the while hoping the collage turns out the way you want it to. I tape the papers to the wall and re-situate them until I like the way they come together. Measure and mark on each paper where the hanger is on the back of the frame. Nail through the paper, remove the paper, and hang your pictures!
For a small collage I pull out the kids butcher paper (again) and cut a piece the size of the wall I want to fill. I lay the pictures out how I want them on the paper then trace the frames.
I measure and mark where the hangers on the back of the pictures are and then hang the paper on the wall.
Hammer through the paper then pull it off of the wall, leaving the nails in place.
Voila! A beautiful collage, and only one nail hole for each picture.