A common method is "sniping." Watch an item until the last minute, then post a bid. It works well if you have two windows open: one with the bid ready to submit (the second "review" screen, not the item screen), the other window to refresh to watch the official ebay time.
I like bidding on things with no bids.
I also put a lot of things on my "Watching" list, even if I don't really want to buy them yet, so I can see how much they go for.
Also watch for other bidders who always seem to bid on the same things you do. That happens to me a lot.