When buying a used car, the first rule is: Don't go alone! Get a friend to go with you. Also, if you decide to buy a car through a used-car dealer, try to have someone recommend a good dealer.
Next, decide what kind of car you have in mind. Consider the different features that you'd like your car to have. For example, do you want an automatic gearshift? Do you want the latest luxury model, or something older?
When you have found a car you like, ask the dealer to let you drive it. Before you make up your mind, you ought to have it checked by a mechanic. If he is satisfied with it, you can then start bargaining with the dealer about the method of payment and price.