I have put together a guide with some (hopefully) useful tips for you readers!

1. Always answer questions from buyers, make sure you check 'My Messages' on a regular basis. You may get questions where the answer is in the listing, the customer has just not read it. So answer all questions and make sure you post them on your listing page. This is a great opportunity to show potential bidders that other people are interested in your listing, and you can asnwer questions others may have.
2. It may seem really obvious but delivery time is one of the most important things for a buyer. I always despatch items the same day cleared payment is received, and my feedback comments often relate to this, and how amazed people are when they place an order Tuesday afternoon and recieve it Wednesday morning. Fast despatch time is essential and key to a satisfying eBay transaction. Place yourself in the shoes of your buyer, and act how you would like to be treated.
3. If you are starting to see an increase in the volume of goods you are sending out, consider shopping around for delivery options. Royal Mail may seem the obvious and first choice, but a lot of couriers out there can offer you better prices for bulky items. To make your items traceable you may want to send Recorded or Special Delivery options. Sellers do get stung if parcels do not arrive, and claiming back from the Royal Mail is a lengthy process. Consider this, are you willing to pay that little extra for each posted item to send Recorded, or will you take the chance and sent all items standard First Class?
4. Set up your automation preferences. Once I have despatched an item, and marked it so in 'My eBay' my customer automatically gets a custom email from me letting him/her know that their parcel is on the way. This saves me a lot of time and lets my buyer know what is going on, Believe me, it saves time answering questions! Before I set this up I was getting a lot of emails asking when items were going to be posted or when items were likely to be recieved.
5. My rule is to leave feedback after I have recieved it. I know some people leave feedback as soon as payment is received, but this is just how I like to do things. Once I have received positive feedback, I know the customer has received their parcel and is happy with the purchase. Consider having a standard feedback comment relating to your shop name or user name.
6. Consider opening a shop if you are selling quite a lot of items. A shop is very easy to navigate from a buyers point of view, as you can categorize your items accordingly. My shop has quite a standard design and I often create promo boxes showcasing my new items, or any promotions I am currently running.
7. Create a 'Me' page. Here you can talk a bit about yourself, what brought you to eBay, and also include a favourite links section, place your main website link here.
8. Get yourself in the Community! Make sure you visit boards, join in the conversations and maybe write some blogs. People on the boards are curious and will take a look at your Me page and see if you are currently selling anything. This is a fantastic opportunity to gain exposure for your listings!
9. Take some time to educate yourself about eBays policies. There are a number of tutorials you can take to get clued up, on things such as Shill Bidding. Navigate around the Help area and teach yourself about how eBay works.
10. Last but not least, enjoy yourself. You may be here to make money or are simply clearing out your home of unwanted goods. As much as I advise you to remain polite and calm, you will get buyers that are hard to please. Keep your cool and do not take things too seriously, or to heart. There will always be people who are impossible to please! I bend over backwards for my customers and offer exceptional customer service, but like to keep things light hearted.

I will happily help you out, just email me if you have any questions, would like some help, or would like to comment on anything I have written about in this guide. I hope this guide has helped you, please vote if so :-)