I always get really pale during the winter, and so when summer finally comes along I have to sun-bathe quite a lot before I get a nice tan. I don't know exactly how long it takes, though, but when I sun-bathe it's usually for over an hour at a time. Being outside in the sun is nice.

Just spend some time outside if the weather's good, and sun-bathe for about 20-30 minutes or so (depending on how pale you are) a day to start with, and then just gradually extend the time you're sun-bathing. We wouldn't want to get a sunburn now would we? :P