In a perfect world, we wouldn't even have to discuss this issue. So take this advice and pretend we're not talking to you, because you've never been in a tanning bed...right? Well, if you happen to stumble upon one don't do it. Just don't. On top of that little thing called skin cancer you're guaranteed to get brown spots, wrinkles, and a big frown from your derm.
This goes for the real sun too. Jailman recommends wearing sunscreen every day (even in the winter), and be mindful of reapplying every few hours when vacationing.