First off, good luck. This event is so much fun, but it's also lots of work. We made about $12,000 on our first auction (!!), but this also included a live auction. A few tips:
Start by writing letters to every company you can possibly think of, and do this soon. You can request a specific donation (e.g., a hockey puck signed by one of the hockey players) or just a general donation. Get teams of people to help you write and send out the letters. Some will respond quickly, others, it will take a while.
If you don't already, get a team of people to help you. Get someone in charge of signing people in and giving them a bid number (definitely recommend bid numbers, not names), someone on refreshments, someone on the items descriptions, etc. If you can preregister people, all the better. Have a table for signing in, and a table for paying on the way out. Have both staffed during your event -- some people may leave after only an hour if you have a lot of items, and they have purchased what they want.
Keep a running list of all the things you have had donated. Best if you can get these into a booklet at least a few days prior to the auction, in a readable list if nothing else. Try to organize the items by some sort of theme, so it's easy for people to search.
We created donation sheets for every single item. It listed the minimum bid, and the bid increment (best to set a general one for most things, and then change any specifics you may need -- for example, items that were worth $1 - $50, we set a minimum bid of $5, with a bid increment of $5).
If you have a web site, list the donations as you get them. The more people can see what you have, the more excited they get about them.
Make sure you leave room in the actual set up for people to be able to see the item clearly, and the bid sheet that is next to it.
We had each table close at a different time. We gave people a 10 minute, then 5 minute, then 1 minute warning for the tables, then counted down from 10 seconds. It made it fun and exciting, and you should have seen the parents hovering over some of the tables!! We had a couple of Palm Pilots donated (worth about $250 each) and the were almost pushing each other out of the way!!
If I think of anything else, I'll let you know. Good luck!