Read as many of the posts on the Seller Board as you can stand.
Remember that most sales are problem-free, the complaints are from the complicated problems or from people who didn't follow the system.
Sell what you know: know what you sell
Pictures are your friends.
Titles are the primary Search tool. You have 80 free keystrokes, use them wisely.
No L@@K, or other dumb words. No useless words like "cute, rare, bargain, vintage'.
Use Brand names but only of product offered.
Include sizes in titles. Include measurements in copy.
Include colour in title.
Watch your spelling. But use intentional misspelling if useful (Tolkein Tolkien).
List in US dollars. Ship to the USA from the getgo. Take your time with overseas.
Don't make excuses, the customer does not care that you are a quadripeligic pregnant war widow who will give all your profits to the cat's home. They just want to pay and get their item promptly. If you think you will have trouble shipping within 48 hours, work on a way to ship within 48 hours and preferably 24 hours.
Well, maybe I'm not a fancy gentleman like you, with your... very fine hat. But I do business. We're here for business.-- Captain Mal Reynolds