FairyJane,
I could give you some simple tips if you lived in my city (San Diego California), but I notice you are in London! I have a few minutes of exposure everyday, and my tan holds, but our climate is still very sunny and warm until December/January. I avoid too much sun, as it has negative longterm effects. I get my sun out in my yard, during gardening.
That leaves tanning products, which i don't know much about, spray tans, and tanning beds. I would never choose a tanning bed, due to the risk of cancer.
I hope you get some more helpful responses...