We both pre-tan before our winter trips. Usually only about 100 minutes, ten ten minute sessions for the 2-3 weeks prior to departure. We both tan easily, rarely burn, and have very few moles/freckles.
We do it for vanity (not wanting to be ghostly white the first few days) and also to lessen the chances of burning the first few days, as we are in the sun and ocean much of the time and even 45 spf wouldn't cut it. The one time we didn't have time to pre-tan we both got burned backs/shoulders the second day there.
While there I use 15 spf, 20 on my face (and I wear a hat in the sun- wrinkles stay away!
).