If anyone wanted an interesting listen on the ins and outs of a car dealership, listen to this recent episode of This American Life. The reporters spent a month with a dealership in Long Island, and the result was entertaining, informative, and a little bit sad at the same time.
http://www.thisamericanlife.org/radio-archives/episode/513/129-cars
The biggest takeaway...go in on the last day of the month. Most dealerships are so desperate to make quota, they'll take any deal, even at a loss. This applies more to new than used, but I still think the last day is the best chance for a deal.
From my own experience, if your dealership is stupid enough to leave their sales board visible, you may gain some valuable insight into who to talk to. A number of years ago, CMP had their board in plain sight. I picked out the salesguy with the lowest number for the month, and dealt only with him. I believe I got a better deal due to his desperation, although I freely admit that my perception could be totally false.