The best salesman in the car dealership is the finance guy. Even when you know the tricks and games, that guy will still get you. You can do some simple research and find out what fees are required for your area/state. Anything beyond that is bogus. You can save yourself hundreds or even thousands by doing the research on this part alone.
If looking used, I'd be sure to buy certified. They'll come with a factory extended warranty longer than the original. GM offered me the original factory warranty with the GMC we bought because it had 1,893 miles. I made them do the certified warranty and it extended my drive train warranty from 60,000 out to 100,000 miles. So keep this in mind if looking used.
If looking new, December is a great month to buy. There's a lot of us TOO guys with trucks that don't have carpet and we love them! You might be surprised how affordable a base model truck is. You don't need a diesel either...but if you want to go out and buy a F350 crew cab dually with a 6.7 powerstroke platinum edition. Go ahead, you only live once!
Yes, have your finances figured out before walking in. Don't tell them though. They'll wiggle more if they think they can make it up on the APR.
I know more tricks but my eyes just got really heavy...maybe tomorrow.