Decide on your budget. Will you finance or pay cash? If financing, how much do you have to put down and how much can you pay monthly with full coverage insurance?
Write out a list of amenities you must have and things you would like to have but are willing to compromise on.
View car listings on sites such as autotrader.com and your local newspaper. Once you have found a car that you like get all the information on the car; mileage, body condition, price. Then go to Nada.com and find out the retail value. This value will be more accurate than Kelly Blue Book should, God Forbid, you have an accident. Print the page or make notes.
View car in person to verify condition. Check tread on tires, open hood and make sure it is clean and fluids are full. Take the car on test drive and make sure heat and air conditioning work. Take car to independent mechanic close by to have a look at major systems.
Ask about warranty. Get any warranties, discounts, service plans in writing. Have salesperson sign his name to it and hold him accountable if there is a problem.
If the car is in suitable condition for the price range, take out your nada information. Never pay more than 90\% of the value listed for your car's condition. Why? If you pull out of the car lot and get hit that is the most the insurance will give you for your car. You have to be able to get what you just put into the car including title, license, and insurance down payment.