Decide what you are buying the car for. Long trips? Smooth rides” Pick up chicks? Need to look good at work? Go for lots of rides at dealerships without talking about money. I had my heart set on something ten years ago, and then when I test drove it – it was awful! Test driving is extremely important.
Then research at Edmunds and ConsumerReports. Get the info on how much every little thing cost. Build your car and price it online or using the consumer reports car pricing sheets. Then when you know what you want to buy, and you know what you want to pay, shop MULTIPLE DEALERSHIPS. Be prepared to walk out with out the car. They will call you and give you a better price. Learn to negotiate.
If you can’t, find someone who can, and have them help you.