Know what you are bidding on. Most online auctions give you at least several days to consider the auction item. Contact the seller for more information or better pictures. Most sellers want the highest ending bid they can get for their items, so they'll be happy to give you more of a reason to bid against someone else for the privilege.
Know how much you are willing to bid for an item. There are a variety of resources on the web you can find that will give you an idea of what an item is worth. Search for the item online to see what commercial sites are asking for the same or a similar item. Set a maximum bid for yourself and don't succumb to "bidding fever". More than once, I have bid more than I would have had to pay retail only to be outbid by someone who had a worse case of "bidding fever". Why pay more than list price for an auction item? Well, some are one-of-a-kind or out-of-print items where this might make sense. If you really have to have it, be prepared to pay outrageously for it, especially if another bidder feels the same way.
Show some courtesy for the other bidders. If it's a maximum bid auction like on ebay, don't try to slick someone out of an auction at the last second. No auction item is worth having other people think you're a sleaze. What's worse is, in your own mind, you'll feel that way about yourself. The Internet is a community. We have good and bad just like in the real world. Which do you want to be? Because people can't see you, the virtual world is a place where you really are judged by what you say and do and not by how you look.
Show some courtesy for the sellers. You can't buy a good reputation, but you can not buy a bad reputation. Pay quickly. (That's probably the most endearing characteristic a buyer can show a seller. Sad, but true.) Be polite and friendly. It costs you nothing, but can bring you two priceless gifts - friendship and respect. There are a lot of people on the Internet who deserve both, and you can be one of them.
Have a good time. What's the point of living, if you don't enjoy it? If you find bidding on auctions frustrating, then find something else to do and save the heart attack for a better cause. If you do enjoy it, remember this when things don't go exactly the way you'd hoped. I've lost out on auctions I really wanted and got goods that didn't measure up to my expectations. On the other hand, I've enjoyed the bidding and I've bought some wonderful items that I never would have found anywhere else. (Some of their pictures can be found on this web site.)
All Right. We've had enough goody-two-shoes philosphy, let's get to the bidding tactics:
No matter what the format, bid the least you can at first just to get into the auction. This will let you track the auction or get information about the auction later on. Let other bidders drive up the price until you get close to the end of the auction. This way, you get to see what the competition is bidding. You may decide that the auction is too rich for you. There's always going to be something else unique up for auction that you're going to have to have. You can't afford them all. (Unless you own a certain software company. If he ever gets into bidding, we're all doomed to disappointment.) Announcing your interest to other bidders can be an advantage or a disadvantage depending on how they react to competing with you. Act accordingly.
If you're in a competitive bid auction where it runs until a certain time has passed without a bid, start bidding seriously that amount of time before the end of the auction. (For example, if an auction runs until ten minutes have passed without a bid after the end time, then wait to bid until ten minutes before the end time.) Remember that bidding encourages bidding. This is good for the seller and bad for you. You may have to respond to quite a few bids, so keep your personal maximum in mind and don't go too high over it. (It would be senseless to advise you not to cross your maximum. You're going to do that. We all do. Just try not to trade your house for a can opener.)
If you'r in a maximum proxy auction, wait until the competition has an hour or two to go before bidding your real maximum. This is fair to the other bidders but doesn't encourage a lot of extra bidding that will drive up the price. If you bid your real maximum at the start of a maximum proxy auction, you're going to be sorry. Over the period of the auction, other bidders will bid against you, see that your maximum is higher than theirs, and bid again until they beat your maximum. This is a form of "bidding fever". It's good for the seller and bad for you. Let's keep this insanity to a minimum by not encouraging it early in the life of the auction.
In a maximum proxy auction, bid odd amounts. I've won auctions within a few cents of my maximum because the other bidders gave up at an even amount. So pick dollar values over 5 and cent values over 50. (For example, if you're willing to pay over $45.00, bid $46.66.) Also, this can confuse the competition. (In confusion, there is profit.)
If you're in an auction with someone in the grips of "bidding fever", get out before they drag you down with them. You're not going to enjoy the results either way. All you'll accomplish is make one of you sell their house to pay for that can opener. If you're tempted to twist their tail a bit by making them bid more (and I've done that, too), remember that you may be on the other side of the "bidding fever" someday. (Mercy may not taste good, but it's infinitely more palatable than pity.)