The basics as a guy who spends a lot of time in the outdoors, both on skis and on a bicycle:
- Wear sunscreen for all daytime outdoor activities, whether it's overcast or not. UV rays can - and do - penetrate cloud layers, especially at altitude.
- Wear a broad spectrum sunscreen that blocks both UVA and UVB rays and is at least SPF 30.
- If you are wary of possibly carcinogenic chemicals, use a zinc-based sunscreen (which may make your complexion a bit "frosted," even the so-called "clear" zinc).
- Reapply often, especially if you sweat or wipe an area of skin regularly.
- Apply to your lips, eyelids (if you don't wear goggles), ears and earlobes, etc. - areas many people miss and that are frequent "first contact" areas for skin cancers.
- Hair cover is not a 100 percent effective sunblock, so on really sunny days it's wise to apply a thin sunblock to beards, mustaches, and exposed scalp hair areas (many melanomas are discovered underneath areas covered by thick hair - it's not UV impermeable).
- When you are done for the day, wash the stuff off as thoroughly as possible.
If you find a sunscreen you like, use it! It can take a while to find one that works, so try many until you find one that suits you.