Congrats on taking this step, definitely make sure you are comfortable with each of the following:

1. Paying cash - you'll want to bring a cashiers check. Have it made out either to yourself, or to the Trustee on the foreclosure you are bidding on. Be sure to bring your drivers license as ID will be required. If you have the check made out to yourself, you will sign it over to the trustee. If the check is for more than your bid, don't worry, the trustee will send you a refund for the difference, usually within 1-2 weeks.
2. Doing your own title research - remember that you do not get title insurance at the trustee sales, as such you'll need to do your own research and essentially "self-insure". Key things to watch for are senior liens, property taxes, and junior federal tax liens. By senior I mean either that they were recorded first, or that were made senior by a subordination agreement. You may find a title company willing to issue a preliminary title report. This would be a good idea on your first deals even if you have to pay for it.
3. No inspections - while generally the inside looks like the outside, you'll want to factor in some contingencies for missing appliances and unexpected repairs. Increase your repair estimates as homes get older and both deferred maintenance and dry rot become more prelavant.
4. Stick to your bid - don't get caught up in bidding, or in what others at the auction may tell you. If it is a competitive bidding situation you should expect the pros to try and get under your skin.
   

Also note that nothing above applies to the auctions of previously foreclosed homes held by the banks. It is easy to tell the difference because these bank auction events are slick marketing events designed to maximize price. The real foreclosure auctions are held on the courthouse steps with no fanfare.