Have you found out everything you possibly could about your items? Try typing their names into a search engine - you might find out something you didn't know. If someone else is selling the same thing as you, then always try to provide more information about it than they do.
Have you got pictures of the items? It's worth taking the time to photograph your items, especially if you have a digital camera. If you get serious about eBay but don't have a camera, then you will probably want to invest in one at some point.
Are you emailing your sellers? It's worth sending a brief email when transactions go through: something like a simple "Thank you for buying my item, please let me know when you have sent the payment". Follow this up with "Thanks for your payment, I have posted your [item name] today". You will be surprised how many problems you will avoid just by communicating this way.