It's all in the psychology for me! I put a bid on if there's none on there, tells potential bidders to "sod off, I've got this one" if they thought they'd get it on the cheap and no-one else had noticed
In fact I tend to just bid the price I'd be willing to pay - I know, it's novel! - and leave it and see if I win. Too easy to get caught up in bidding wars.