In most cases, oily skin can be treated at home. However, you'll want to call a doctor if you develop acne that doesn't respond to home remedies or notice any sudden and/or unusual change in your skin (if it goes from dry to oily seemingly overnight but it isn't time for your period, for example). Otherwise, first try keeping skin squeaky clean.
As anyone with oily skin knows, the oilier the skin, the dirtier the skin looks and feels. To help combat this feeling, it's important to keep the skin clean by washing it at least twice a day. Some doctors recommend detergent-type soap. You might even try adding a drop or two of dishwashing detergent to your regular soap; the extra kick will act as a solvent for the oil. However, other dermatologists say detergent soaps are just too harsh even for oily facial skin, recommending instead twice-daily cleansing with a glycerin soap. If you try a detergent soap and find it too irritating for your skin, try the glycerin variety, generally available over the counter in the skin-care aisle of most drugstores.