This will probably be the easiest guide there is. 

1.  Disclose EVERYTHING you know and can see about your product if it is in USED condition. Don't be afraid to disclose a flaw-in fact, I make a section that says FLAWS: and list whatever I feel might be of concern to a potential buyer.  Believe me, if they really want what you're selling, this will only encourage them to buy your product since they will already feel they're dealing with an honest and up-front seller.

**When writing your ebay ad, make sure your title contains "KEYWORDS" that will be picked up by search engines. That way you'll get way more coverage across the Internet.  Ebay uses google search engine amongst many and keywords are very important to drive traffic to your auction. Keywords are nouns - not descriptive words, but words like bag, purse, ring, and anything else you can think of without spamming with a bunch of label names or company names.

2.  DON'T SELL FAKES OR COUNTERFEITS OF ANY KIND!  And there are a ton of them on eBay.  Ask a seller to prove authenticity and they try to skirt the issue.  If you think the buyer won't catch it - THEY WILL!

3.  Follow the golden rule of sales...ALWAYS THANK THEM FOR THE SALE AT CLOSING!! Selling on eBay is no different then at a store, you just can't see your buyer, but the rest is still the same.

4.  ALWAYS leave positive feedback AFTER you have received yours and include THANK YOU again.  Believe me - it works!

5. Don't be afraid to give free shipping to repeat buyers - if you have what they want, they'll come back again and again.  Be a fast shipper, communicate after you've received payment, use Paypal's system for making labels and get a free delivery confirmation number by using them for your USPS or UPS labels. Tracking numbers are great - you can also get them free by using USPS.com direct when printing up your shipping labels. 

6.  And last but not least - be fair on your shipping charges.  I see so many sellers charging huge amounts for shipping and they call it handling fees and then you receive the item in a used flimsy file folder box. Use quality materials, it's okay to recycle cardboard boxes if they're decent. Don't be afraid to use bubblewrap and DO NOT ship an item without some kind of packing material.  No buyer appreciates that for the money they pay for shipping.  AND it could damage the item and you'll have a loss on your hands.