On a beach, the sunrays not only reach your body directly but are also reflected by the sand and the water. This increases your chances of getting damaged by sun very substantially on a beach. It is better to take as much protection as possible while picnicking on a beach.
As we go up on a hill, the sun damage increases. So while trekking on a hill or on a hill station, take maximum care with protective clothing, sunscreens, sunglasses and umbrellas.
Snow intensely reflects sun radiation. Protect yourself with in as many ways as possible. Wear tightly woven clothes, which cover your body from top to toe. Wear sunglasses and a hat (or use an umbrella), apply higher SPF sunscreen on all the exposed parts, preferably the whole body.
Many of us think that a cloudy day is safe to roam out. Do you know that UVA rays can pass through the clouds? So take protective steps even on a cloudy day.
Try to remain indoors between 10 am to 4 pm; not only during summer, but also during winter. But if it's inevitable, use enough protection.