Melanoma is the most common type of cancer in 12-24 year old Australians (Cancer Council). The MyUV website can tell you the UV level where you are and recommend the times you should take precautions. Your skin also ages prematurely when exposed to the sun unprotected.
Slip on protective clothing like a rashie or shirt
Slop on some sunscreen UV30+ or higher
Slap on a hat - preferably a wide brimmed one
Seek some shade
Slide on some sunnies.