Really pay attention to the winning bids, especially early in the draft......Auctions are a zero sum game......if RBs are going for more than what you thought, that means another position will be going for less. Adjust your values on the fly.
Agree with an earlier poster in that don't get caught bidding on the last player in a tier....they usually go for more than they should.
But you have to win some studs, so get in there and bid. I see some owners that try and build a very deep team of 2nd and 3rd tier guys......these owners generally will never win the title. IMO, there are 9 or so elite fantasy players......Foster, Rice, McCoy, Rodgers, Brady, Brees, Calvin, Graham and Gronkowski. Make sure one of these guys is on your team.....2 of them even better.
Run it Up suggests never nominating a player you want early. I disagree. I like to mix it up so my leaguemates can't read my true feelings on a player. I sometimes like to put up a mid tier player that I really like up for bid very early. Say you really like Matt Ryan this year (many do) and you think he's worth $5 more than his "market" price. Nominate him early and see if you can steal him at a discount, since many owners want to save their cash for the stars.
I like to get in there and bid on a lot of players, up to a certain amount, even if I truly don't really want the player. I never want my leaguemates to know that when I get in the bidding that I REALLY want that player.....but.......be careful when running up the bid for players that you don't really want. I saw a guy who drafted Drew Brees run up the bid for Eli Manning and got stuck with him when the other two bidders bailed. He wasted $15 of his cap which he could have used on RBs/WRs. Key is, if you really know your leaguemates well, you can make then overspend for players that they really want.
My key trick to doing well in an auction is to budget EVERY roster spot. I don't think it's enough to just say I want to spend 40% on RBs, 20% on QBs, and so on. I look at my projections and the "market" rates for each player (use mock auctions). Then I put together a strategy that optimizes my team. Then put together a budget for each spot.....$15 for QB1, $30 for RB1, $15 for RB2, and so on. Make sure that you have at least 3 options at each roster spot, to give yourself the best chance of executing that strategy. So for QB1 my list may be Ryan, Rivers, Romo...while for RB1 it's McFadden, Forte, and Chris Johnson. So if I have a 17 player roster, I generally targeting my team coming from a list of about 50-60 players. Now that doesn't mean that I won't buy a player not on this short list if the price is right......you have to be very flexible in an auction. But you can eliminate a lot of players simply because they are overpriced to your expectations.
And last but not least.......try and save some $$$ at the end. If you have some cash left when others can only bid $1, you can steal the good sleepers. There are always some good players that slip through the cracks that you can pick up for cheap since you have the money to spend. In one draft Brandon Marshall was the 120th or so player to be nominated......most owners had very little money but I had enough to snag him for only $6 in a $200 cap.