My words of advice, worth what you've paid for them...
Know what you're looking for -- no only price, but rarity, usual flaws, that kind of stuff. Know how much you're willing to spend.
My usual practice when I see something I'm interested in is to place a nominal bid on it right away.
My next step is to set up a snipe for the last few seconds of the auction at my max price. Gixen.com is my current friend for snipes, and is free.
How much I'm willing to pay is a function of many variables, including how often I've seen the thing of interest come up for auction, and what I've seen them going for, as well as how much do I *really *want* this thing?
For some things, I track prices to see what folks are getting. That helps me recalibrate my price range, sustain my price range, or decide that the lot of 'em are nuts and to look at something else.
Look for misidentification and misspellings -- yeah, everyone is looking for the seller who doesn't know what they've got, and they're letting it go for a pittance. But sometimes they do know, and they know it's dixie fried. Examples -- Bird wattmeter slugs can be damaged by dropping them. HP 848X power sensors have no sense of humor whatsoever when it comes to high power levels. You undoubtedly know of similar items you wouldn't bid on or by without some guarantee they work.
Be patient. It took me a number of auctions and a number of months to get one piece of gear for the price I was willing to pay.