1. Fill the title. Use relevant, searchable words - just because "everybody" knows that
Morgan dollars are silver won't capture the potential buyers who search for "silver" to invest. The title is where you're going to generate 90% of your Search results.
2. Good pictures are
imperative. If you can't get a clear photo of at least 400 pixels, then post a scan. A poor photo causes the discerning buyer to click "back."
3. Write a clear, concise description. Don't include six paragraphs of boilerplate history - you'll bore the buyer. Some of my listings are two sentences. Uze the spelchek.

4. Have a reasonable return policy. I've offered a 7-day return policy since 1999. Never had to use it. Not once.
5. Time your auction to end in primetime on the weekend of your target demographic. I end US coin auctions at 8-10PM EST on Sunday; Australian and British coins get timed to end appropriately in their respective countries, even though the likely buyer will still be American. That's a gesture of respect that will bag an International buyer when you might not otherwise.
This rule isn't so important for established sellers who already have a clientele - I probably don't need to do it any more - but as a new seller you want the most possible "accidental" customers in front of the keyboard when the auction ends.
ebay traffic (according to Alexa) spikes every Sunday.
6. Free shipping is a nice touch, but if you want to be compensated for shipping, or your margins are small, charge as little as possible. I'm sorry - as a buyer I don't want to compensate you for gas spent running to the Post Office - so don't add "extra" charges above and beyond exact shipping. Generally, I make Insurance mandatory, but even if I don't I pay for Insurance whether the buyer wanted it or not. Anything worth over $20 is worth Insuring.