Sometimes there are oil glands which get overworked, get enlarge, and produce too much sebum. The sebum can get trapped in the hair follicle. When this happens the pores get clogged and black heads or white heads form and the bacteria start to multiply at an alarmingly fast rate.
However, there are things that you can do that really will help. The first thing you can do is to wash your face with a mild soap or a sulfur based soap. Wash your face with just your finger tips. Don't ever use a wash cloth as it holds germs and bacteria. Rinse your face with clean water several times to ensure you remove all traces of soap, and then pat it dry with a clean towel. Do not rub your face with the towel and never use the same towel twice without it being clean.
Take a good multi-vitamin and multi-mineral supplement every day and drink at least 8 full glasses of water (not soda) every day. The vitamins and minerals will supply nutrients that are absent from most diets and the water will help to hydrate the skin as well as to flush toxins out of your system.
If you use over-the-counter acne medications, be certain that you follow the directions carefully and that you use a good sunscreen when you are outdoors as some acne medications make the skin more prone to sunburn.