How to prevent pimples from growing on my face?

Cleaning & medicine. For the little pin sized pimples, usually cleaning one or two times a day for a couple of weeks with an otc product from benzoyl peroxide (proactiv, zapzyt, panoxyl and others) is enough. If not you can add salicylic acid, resorcinol or sulfur products (various neutragena, clearogen, clearasil and others). If you have large/cyst like pimples these will often need more- see your family doctor.