When you go outside, wear sunscreen. You should be wearing at least SPF15 every day in your moisturizer anyway. Try to avoid purposefully tanning. Stay in the shade. The only way to get back to that, it sounds like, is to let your tan fade.

Exactly what caslynn said. Be sure to wear sunblock, one with zinc oxide will protect you completely (shiseido makes one) . You can try to exfoliate the skin to quicken the process of the tan fading because some tans start to accumulate overtime and become a perma-tan. Likas papaya soap or Kojie San soap should help you to get back to your birth colour and remove all the tans if you use them with sunblock and practice sun avoidance protection.