Use a cleanser daily that is manufactured to fight acne. Make sure your diet includes lots of water, fruit and vegetables. Try not to pick at any places on your skin where pimples and whiteheads are developing. Get lots of sleep.
One of the best methods that works for me is regularly using a face wash that contains salicylic acid. If this dries out your skin, you can also use an oil-free facial lotion.
There isn't a whole lot you can do to prevent acne. About all you can do is keep your skin as clean as possible and that includes removing make up after several hours of wear. If acne becomes severe a dermatologist may be able to give you some kind of cream or medication.
They might appear because of the heat if sweat excessively on your face and you should try some face cream that has ingredients that block and control the sebum secretion.