Howmuchisenough has very good advice. Only thing I would add is I bid last - meaning, I don't start bids, I let the price get established and then start bidding at the end very agressively.

As advised above, talk to the auctioneers ahead of time so they know what you are looking for and what you look like. Let them know your signals of a bid . . .   

I too have used the double or triple bumps at the end to get the other guy out . . . auctioneer seemed to like that for some reason ; )

I have my price set in advance and never go over it. Never.

If the land is split into parcels - and then bid all as one parcel, Never, Never bid the seperate parcels if you want it all. Only bid on the total parcels. No need to run up your own bids. Guys have done this . . .  thinking they only want the one parcel or maybe two parcels and then due to pricing, state bidding on all parcels - never understood what the heck they were thinking . . .  

Edit: One last thought - I've asked for a reduction of commission (buyer / seller commission) and used that to increase my bid. Ask the auctioneer to reduce his take, it never hurts to ask . . .

Good luck. It can be a fun time . . . .