SPF 30 is great. Some sunscreens leave some stupid streaks on your skin so be sure to use sunscreen made for black skin. Also, while the face shows damage quicker, remember to protect your arms and legs and places usually exposed to the sun.
Heading to the beach? Rock a hat. Get baseball ('face') caps for your commute even if it does not match your outfit. You can keep it in your bag then wear when you are trying to get a cab or bus.
Plan your day and movement so you are not getting the sun at the worst.
Don't throw shade, get under the shade. And rock some stylish fashionable shades.
Of course I can't take my advice re: the latter since I wear recommended glasses, but you can always get your prescription put in some shades, or go for photocromic lens which will go dark and protect you when the sun is out.
If your skin HAS been damaged, it's time to fix this.