Kathy makes a good point, these tanning beds have a bad rep (as dones the sun) and some people have lifelong consequences for using them.
You did ask the question though, so I'll tell you what I do. About 6 weeks before vacation, I tan. I buy a minutes package as the session pkg is usually higher and a session can be up to 20 minutes. I could never do 20 min. I start out with 10 and do that about 3 times a week for about 2 weeks, then I bump to 12 for a couple of weeks (try to do at least 2 sessions per week) and then 15 for the next couple of weeks before we go.
I to am very fair, sensitive skinned and I also have bad reactions to sun screens. So, as another poster mentioned, it helps me build a base tan so I don't get so scorched while on vacation.
I keep tanning to a minimum because I'm aware its risky business. Having said that, I love tanning. I love the lay down beds, turn on the radio (or sometimes just quiet) and soak up the warmth for ten minutes. I live in Wa state, light and warmth is at a premium in these winter grey months!!
Jenn