Wear sunscreen every time you go outside. Even when it's cloudy, you're gonna get burned. Skin cancer is really easy to get. Chose a sunscreen with 30 SPF (Sun Protection Factor) or higher and reapply every hour. You can even buy lip balm with sunscreen because your lips can get burned, too!
Go for the natural look. Get some waterproof mascara or just go without makeup (watch out, though -- to much waterproof mascara will dry out your lashes). You probably won't need much blush if you're running around and getting hot, but dust some over your eyes for a pretty look. Chapstick or lip balm make your lips look effortlessly lush.
Smell good. Get some fruity deodorant and some fruity body spray with a light summery scent.
Get a summer haircut. Adding layers gives your hair more volume while making your hair feel weightless.
When you plan on getting a tan, put a heart sticker on your ankle. When you're done with the sun, remove it and viola! You'll have a pretty heart design without getting a tattoo.