I am surprised at how many people still believe this sun myth. Multiple studies have shown that a base tan offers no significant benefits in preventing burning later on. What's worse, the UV damage the skin takes on from this practice, especially if done in a tanning bed is both measurable and risky.
Think of it this way. The tanning response, (production of melanin) is triggered by too much UV exposure in an attempt to protect the DNA inside your cells.
When you tan, it is literally a cry for help from your skin cells.
Skip the base tan and practice smart sun behavior - wear a minimum of SPF 30, limit exposure between 10AM and 4PM, and utilize hats and SPF clothing. Your skin will thank you!