I agree with Dukester.
First of all define a maximum price you're willing to pay for the item, your maximum bid will be that price, with postage charges deduced.
Now, put the item on your watch list and don't bid right away. Save your bid (the maximum bid calculated earlier) for the last 10 seconds. If the item is really important to you, don't wait as much, sometimes glitches happen and you lose the auction.
There are some things you can do to improve your success. First of all, be sure that you're logged in and you've ticked the checkbox to keep you logged in. I've lost one auction cause my session expired in the last minute. To make the actual bidding in the last seconds open two windows with the item page and put them side by side. Leave the first one for refreshing the timer and in the second put your maximum bid and go to the confirmation page.
In the last seconds you just have to press the confirmation button on the second window.
There are a couple of reasons why you should not bid before the last minute.
First of all it tells all your opponents that you're interested in the item (if the auction reveals the identity of the bidders). They can check your past purchases and if you're bidding on similar items. They can even profile you to understand what kind of bidder are you. If they see you're a sniper, they will most probably try to outsnipe you. Sniping a sniper is very satisfying
Secondly, it reduces the chance for a bidding war and improves your chances on getting a cheaper price for the item.
Don't forget that an auction is a game and people can buy an item just to make you the loser.
There are a lot of articles and books on ebay strategies and techniques, just check google:
http://www.google.pt/search?q=ebay+early+bid&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a