Use a gentle facial cleanser twice a day. Most dermatologists agree that cleansing the skin is the best way to reduce oil.[1] Make sure to use a gentle, pH balanced cleanser rather than regular soap. Most soaps are highly alkaline and strip the natural acid mantle from the skin leaving it vulnerable to bacteria.
Products containing benzoyl peroxide, salicylic acid, glycolic acid, or beta-hydroxy acid are often considered best. These are slightly acidic, however, so start off with only a small amount to make sure your skin doesn't have an adverse reaction.
When washing your face, make sure you use warm water, not hot. Hot water can further irritate the skin.