The medicine you use depends on the severity of the acne problem.
Make sure you get a little sun, but not too much, and get a good amount of sleep. Wash your face regularly.
Then, there are acid based topical medications with the ph somewhat off that can also prevent acne.
The cosmetician that I trust the most and whose products and product recommendations I would look at are Paula Bedgoins' at www.cosmeticscop.com
She sells products and reviews other people's products.
There is no reason to go "natural" in products because natural products often don't work as well and are more irritating to your skin, and usually aren't actually natural anyway. Natural in no way means safer or better.
If these don't work your acne may need to be treated pills or a strong topical medication that you would get from a dermatologist.