1. Check the seller's feedback. If he has a large number of
feedbacks and 98%+ are positive, then your odds of a good transaction
are good.
2. Check item location. Make sure it's not in China or something.
3. Check shipping charges, make sure they're not going to charge $20
or something.
Already have your PayPal account set up before bidding on eBay, and
be sure you set up PayPal with the address you want things shipped
to. PayPal and eBay sellers get cranky if you change shipping
addresses on them.
Other than that it's a piece of cake.