There are several different things to consider when bidding on land at an auction.  I speak from a position of having made many mistakes versus being an expert. Here are a few things I have observed through the years. 

1. If you are bidding against someone and get down to the "short rows" hit your next bid quickly.  Typically, waiting to counter the other bid is a sign that you are getting close to your limit or really don't know what you are going to bid.   This just gives encouragement to the competition.
2. If you really want to get the competitions attention wait till you are near the end and bump the bid 2 or 3 times what the increments have been.  Many years ago I bought a farm at auction.  We were making  $1,000 bumps and the price was getting pretty high.  I bumped the bid $4,000 and the auction was over.  Later I was talking to the guy I was bidding against and he thought the $4,000 bump was a by bid so he quit.  Wound up selling him the land a couple of years later.  Made a little money.  Dumb luck on my part. 
   
3. In regard to the above my preference is to keep a low profile at an auction.  Usually prefer that no one knows I am bidding.  Usually talk to a bid taker before the auction starts and tell him I am interested and to keep an eye on me but don't talk to me.  Bids are made with very discreet gestures such as a wink or subtle head nod.  You know you are doing things right if you can be talking to someone at an auction and they don't even realize you are bidding. 
   
4. There is one exception to discreet bidding.  Have read some posts on here where others at an auction have not bid against a young person wanting the land.  Use your judgment on this one. 
   
5. The biggest no no I have observed during an auction is don't get into a personal bidding war with someone where it becomes an emotional battle versus a business matter.  That goes back to point 3 about keeping a low profile. 
   
6. You can even have someone else bid for you if there is definite need for no one to know that you are bidding.  Goes without saying that this needs to be someone you trust.