Clothes for sun protection: The best garments for sun protection are those that are labeled as "UPF" (ultraviolet protection factor). The higher the number, the less UV light is let in. For ordinary fabrics, it's best to wear light colored clothes that reflect more light. Darker clothes absorb more light. Heavier, tightly woven fabrics are better than sheer or loose weaves. Better to wear loose clothes than tight fitting garments.
"I need to be in the sun to get Vitamin D.": The body does manufacture a certain amount of Vitamin D from UVB exposure, but overexposure to UVB causes Vitamin D destruction. So the best way to get Vitamin D is to eat foods rich in Vitamin D. These include oily fish such as salmon and fortified dairy products. Supplements can also provide the recommended amount of 1000IU.
"You can't get burned on a cloudy day.": This is absolutely NOT true. 77% of the sun rays penetrate the clouds. So wear SPF "rain or shine".