Your first stop should be eBay's Guide to Seller Services http://pages.ebay.com/help/sell/services.html
eBay's Seller Central has all the resources you need to learn about the basics of selling on eBay http://pages.ebay.com/sellercentral/index.html
The key to a successful eBay selling is simple -- Sell products that people actually want.
If you want to earn serious money from eBay, you need to have a well-thought out business model. Selling on ebay is getting tougher -- just look at the number of auctions that closes without a bid. Go to the boards on ebay and you will hear even oldtimers complaining about how stiffer competition plus higher fees make it so much harder to sell on ebay.
One success model of ebay is the couple Jay and Marie Senese (username jayandmarie) of the 1-cent CD fame. They have the highest positive feedback number of all sellers on eBay. Their business model is to buy very low cost CDs in bulk (those that CD stores sell in their discount bins) and offer them on ebay at a starting price of 1 cent http://www.businessweek.com/magazine/content/04_23/b3886080.htm Their success is based on the fact that they stumbled on a sustainable business model with products that people really want.
eBay has several ways for you to determine exactly what the hot items to sell on their marketplace:
Items In Demand = the most popular items currently within that particular category. To see the In Demand page, go to http://pages.ebay.com/sellercentral/sellbycategory.html
Hot Items by Category Report = a monthly report that lists the fastest growing categories on eBay for the previous month. Go to http://pages.ebay.com/sellercentral/whatshot.html and select "Hot Items by Category" from the menu on the left.
eBay Pulse = "a daily snapshot of current trends, hot picks, and cool stuff on eBay". Go to http://pulse.ebay.com/ to see eBay Pulse in action.
Merchandising Calendar = eBay promotes specific categories on its home page each month. Savvy eBayers know that this home page exposure results in more interest in such categories. Go to http://pages.ebay.com/sellercentral/calendar.html to view the current Merchandising Calendar.
As for items to sell, you can:
1. Buy bulk liquidation items such as those at Liquidation.com. The capitalization may be big, but the idea is to sell the items individually and profit from it.
2. Find manufacturers of items you want to sell and buy discounted items from them
3. Make deals with retailers in your area, and offer to buy their unwanted items for deep discounts. jayandmarie - the most successful ebay sellers - made deals with music stores where they will buy the entire inventory in the discounted bins, and then sold the items on ebay for 1-cent starting bid.
4. Look for possible partners on the Web, preferably outside of the US. Import items from them and sell them on ebay. There's huge profits to gain from this approach.
5. Check out deals from outlet stores. Focus on brand names, which you will find to be easier to sell.