I always look to bid on no reserve auctions ONLY.
Most auctions I see where seller sets a reserve are usually overpriced and don't sell.
Don't bid early in the auction... you are only raising the final price.
Wait towards the ending time, see what bid is then, and then decide if you want to raise that bid.
I see what I consider "clowns" placing a bid on a 10 or 13 day auction on the first or second day. Some people have no concept.
I've gotten lucky a number of times on GB. Misspelled auctions usually work in your favor, as others may not find it as you did.
Also, auctions that end in the middle of the night or midday when most people are at work, offer better chances to snag a good deal.
As previously stated by some, don't bid if you see lousy pictures. It's a great way for a seller to disguise true condition. Ask for them to email some good, clear pics to you, and if they don't, move on. Most honest sellers will place clear pics with honest description. I've found most sellers on GB to be honest.