9. This is a tip I haven’t found in any other string-art tutorial, but it’s key: Use a nail holder to hammer in a nail in each pre-drilled hole. (See the supplies list for sources.) It holds the nail straight, it’s small enough to get in tight spaces, it keeps you from hammering your thumb, it speeds up the work significantly, and it automatically measures the perfect height of each nail for you. Just hammer down as far as you can, remove the nail holder, and, voilà, all your nails are straight and at the same height. For the ornament nails, don’t hammer them down all the way. I kept them about ⅛ inch taller.