1. No stealing art.
2. Be respectful to the artists and their decisions. If they say they will not draw you, leave it. Do not harp on them.
3. Follow ToS and no spamming on the thread. A bump or two might be nice to keep the thread up, but hundreds of them are annoying. :]
4. If an order doesn't turn out how you expected, tell your artist nicely. Do not be mean about it.
5. Follow the procedures the artist you have chosen has lain out.