The best piece of advice I can offer for hanging multiple pieces of artwork is to create a paper template. If you live alone, it allows you to step back and rearrange the pieces until you are happy with the result (be sure to use blue painter’s tape to avoid harming the finish on your walls), and if you live with someone, you can avoid the domestic disputes that are sure to arise when someone drills a hole in the wrong place.
Brown craft paper, the Sunday comics, or anything large enough to represent the pieces you want to hang will do. This is especially handy if you want to hang work at unusual heights (over a particularly tall piece of furniture, etc.)…live with it for a while and see if it works for you. If so, you can finally pull out the hammer and nails and get to work.