Another tip, although some people don't like the concept, is to use a Sniping service. That is to place a maximum bid which the sniping service enters in the last few seconds of the auction. That way you will never pay more than YOU think the item is worth and if somebody is willing to pay more you don't win it. This saves you getting into the "I must have" syndrome.
I use and free sniping agent called GIXEN with eBay.
Hope this helps.
Oh and for those who wish to slate me for "cheating", remember if you put in your maximum bid and lose the auction great, but if you must insist on chasing a bid buy upping the anti everytime someone over bids you then don't be surprised if you get snipped.