Unless you are born with dark skin, I can't think of a healthy way to do that. Tanning salons and over-exposure to the sun do damage to the skin, putting you at a higher risk for skin cancer as well as premature aging - wrinkles, "age" spots, etc. Taking good care of the skin you have (cleaning with a non-drying cleanser, using sun-screen, avoiding the sun) is probably better than trying to maintain a tan.