Do plenty of research on eBay before listing. Have a look at completed auctions and see how much similar items have gone for in order to set realistic starting prices. Look at listings and see how other people have described your items - pinch any good ideas! (But don't lift it word-for-word.) Make sure you list in the best category for your item - it can sometimes be worth including it in 2 categories. Take a good photo (or two) with a non-cluttered background.