How much money have you saved for the car purchase?

If you buy a used car take it to a mechanic for a pre-purchase once-over. Even if you are buying from a dealer. Make sure you compare what you are buying to other cars of the same year, model, mileage. Test drive the cars you are interested in. This includes driving slow, fast, on the freeway, making turns, going in reverse. If you have to take along a salesperson have then be quiet so you can listen to the car. Don't let them blather about how wonderful the car is. Notice whether the car pulls to the left or right (with hands barely on the steering wheel). Brake hard. accelerate hard.

Do not buy extras. That's where dealers make their money. No extra warranty, no extra coatings, no rust proofing. You will be pressured and have to say no about 50 times. If they get too annoying start to leave. They hate losing a sale.