Bid Early and Bid Often
Otherwise known as sucker bidding!
There are good reasons NOT to bid early. Here are two:
1) You instigate others to bid higher, earlier. If you wait until the end, they don't have time to outbid you when they see your higher bid.
2) If you're known in the X collecting community to bid on X, they can track what you're bidding on. What if you found an X because the main word was spelled incorrectly (i.e. typewritter instead of typewriter)? Maybe the other collectors wouldn't have found it, but because you did, and bid early, now they see it too!
MattL: Regarding your early bid question, if two bidders enter the exact same amount, the earlier bidder will prevail whether they bid on the first day of the auction or the last. However, if you are not the earlier bidder and you bid the same amount, you will immediately see that you were "outbid," so to speak, and can bid again. When you see the high bid is the same as yours, you'll know you only need to go one increment higher to beat them.
Remember, if you place a bid that does not exceed the existing bid plus the designated bid increment, you'll be told the bid does not meet the increment requirements, as in Allen's example above. Say the increment is $0.25. You see the bid is at $10.00. You want to bid $11.25. During the few seconds between you seeing the "last" bid and bidding, someone else places a bid of $11.01. Your bid will be rejected, because the minimum acceptable bid after $11.01 would be $11.26. At this level it sounds a little ridiculous, but I've seen this happen on eBay in the four-figures range!
Now, Say someone bid $13.26 on an item with a $9.99 opening bid, and the bid increments were $0.25. It would show a $9.99 bid. If you bid $12.99, they would be high at $13.24. If you bid between $13.01 and $13.26, they would be high at $13.26. Since the increment they were high at was less than $0.25, you'd know their highest bid was reached, and could bid one more increment. However, if the high bid was still $9.99 when you bid, and you bid $13.27 or more, you'd be high. Your bid beat the $0.25 requirement for the current high bid of $9.99. You don't need to beat their highest entered bid ($13.26) by a full bid increment if you've beat the high bid shown ($9.99) by the increment.
So, a secret I use is to always bid a few cents above an increment. For example, instead of placing a high bid of, say, $22.99, I'll bid above that bid to $23.01 or $23.03. Lots of people bid $XX.99 or $XX.00. Just a couple of pennies can make a big difference, as other members have seen!
Good luck,
Chuck