When it comes to waxing a car there are a couple of important things to know. The first is to make sure that you start with a freshly cleaned, but also dry car. If your car isn't spic 'n span any dirt will be rubbed into the paint, leaving scratches. You should also avoid working in direct sunlight as wax can stick to a hot car, making it harder to remove and possibly damaging the paint.
The second is to choose the right wax. If your paint is still in good shape, it's best to go for a straight wax that doesn't contain any cleaners or polishes. Using a straight wax you can wax your car as often as you like with little risk of damage. If your paint has light scratches a wax with a cleaner or polish might be worth a try, but they should only be used when needed, and no more than a few times a year. Using a liquid (typically polymer based) or a paste (usually carnauba based) is largely a matter of preference. Generally liquid waxes are easier to apply, while paste waxes sometimes provide a better finish.