Tips for car shopping:
Don't focus on the monthly payment. Salesmen will use as many years on the car loan as needed to get you in that new ride. Let's say your budget is $450/month. It won't work on a 4 year loan, but they can do it on 6 years. You fall in love with the car....and they got you hook, line and sinker. Focus on the total cost and negotiate that....then see the payment breakdown. Be ready and willing to walk away.
Next, visit local banks and credit unions to see what kind of loan you can get (check those interest rates). Perhaps ABC Credit Union can give you a $25k loan at a much better rate/terms than the dealer. If so, use that financing offer from the credit union and see if the dealer can match or beat it. Obviously if you have a shytload of cash, just find a nice used ride and pay cash.
If you buy used or new...make sure you get some kind of bumper to bumper warranty that covers drivetrain, powertrain etc. Pay more upfront but avoid expensive headaches down the road. This is especially true of cars that are known for reliability issues (mid to higher end German and British rides, certain American brands etc.).
Walk away. Don't buy a new car when your current ride is literally about to break down. Sometimes you need to do extra research and shopping. Dealers can tell when you're anxious and will play on that. Of course sometimes it's good to pretend a little bit. If they think you're close, they might sweeten the pot to close the deal.