We sell tons of stuff on ebay. Search for the item you want to sell and watch the auction. See what price it got to when the auction is over. That will give you a good idea how much you can probably get.
When you actually set up an auction on ebay, it usually pays off to start the auction at a low price (like $1), especially if you are competing with other sellers. The low price will draw people to your auction and they'll bid on it instead of the competitors' auctions. We find that by starting it low, the ending price is usaully higher than if we started it high to begin with.
If you really do not want to sell the item below a certain price, you can configure a "reserve" price. This price is not visible to the bidders and it allows you to back out of the sale if you don't get as much as you want. However, having a reserve price may detract bidders from your auction.
So I think it's best to have no reserve and have a low starting point. If you are uncomfortable doing this, configure a reserve price. That's better than starting high, IMO.
Oh yeah, definitely write up a good description and take photos. I sometimes see auctions with no photos -- major mistake.
Lastly, you may have a hard time selling items if you haven't used ebay before. You start with a zero rating and people will be wary of buying from you since you have no history. You might want to BUY a few items on ebay to get your rating up before you try to sell.