I haven't sold anything myself, but from my
experience as a buyer, I can offer one good
piece of advice that I haven't seen offered yet:
make sure you have your images up on a decent
server.  There are a lot of auctions that I've
seen that I might've been interested in, but the
picture doesn't load or loads so slowly that I
either give up on it or decide to try again later,
which I usually forget to.