Definitely take a check list with you like one of these:
http://www.samarins.com/check/index.html
http://autos.msn.com/advice/articles/aischecklist.aspx
http://www.life123.com/career-money/...hecklist.shtml
You may not understand exactly what you are looking for half the time, but they will know you mean business and hopefully won’t rip you off. Plus some of these things I would never think to check. I used one of these before when car shopping, they can be really helpful.
And like someone else suggested, get the CarFax on the car before buying it.