Grab a high factor, because being brown are you getting anyway. Also, your beautiful brown skin will stay longer brown if you apply your body with sun protection before you go in the sun. So feel free to use a factor 30.
Sunscreen is often too fat for the skin on your face or you find it too sticky. Get aface cream with SPF 15/30. Preferably as high as possible. Your face becomes very much exposed to the sun and therefore it is the best to use a cream every day during the summer that contains an SPF factor. But you can always buy sunscreen that is specifically for the face.
Keep no consecutive hours sitting in the sun, but also go looking for shadow. So get out of the sun especially if it feels too hot or irritating to the skin. At 12 till 3 hour, the sun is very hot so sit down around that time in the shadow.
Don't forget hard-to-reach places. Don't forget to cover the backs of your knees, back of your neck, elbows and back of your ears (if you have short hair). Feet should also be included if you are wearing sandals, flip-flops or going bare-foot. Even these places can hurt a lot with sunburn.
Put a small amount of oil or sunscreen in your hair so you will avoid burning your scalp. Or cover it with a hat. Some shampoos and hair conditioners contain SPF protection.