Now I don't claim to be an authority, or a frequent "ebayer", or a powerseller but over the years I formed my own ideas about what makes a good ebay seller.
1. Be honest with your listings, if the item is damaged, or you suspect something does not work properly, or there is a small mark or scratch, make it clear in the listing. Equally if you have pets or smoke then it is likley that your item will reflect this in some way.
2. Be a good communicator, this does not mean you have to be stuck to your laptop, but if you respond to all emails and update listings with relavent feedback, then the bidders know that you are care about what you are selling, and what you sell has been cared for.
3. Be price aware, if your starting price or buyit now is excessive, this can annoy bidders are they can find out very easily reasonable comparisons and then make a quick judgment on your item, and you as a seller.
4. Be helpful, sometimes things go worng, and if they do its better to deal with them as quickly as you can, even if you feel it is not your falut, sorry I mean fault :-)
Finally, Be Happy and a wise ebayer ...