There are a lot of ways to create a gallery wall. Some people like to lay everything out on the floor and arrange it, then mark off spots on the wall. I just started hanging. I randomly hung up three of the larger pieces first then started filling in around them with smaller pieces. I think this is the least complicated way to do it if you're ok with a little randomness in spacing. I ended up only having to adjust two nails.
Most of the pieces on this wall were handmade by Zach, myself, or a family member. There are photos, drawings, and paintings done by Zach and me, a piece of embroidery from my grandmother, and photographs taken by my uncle. I didn't change out anything in the frames, everything just seemed to go together. Despite my love of white decor, we sure have a lot of dark framed pictures.