At your age (and mine), the most important thing is sun protection. It is SO important to use sunscreen all the time! Protecting yourself from UV rays now will help to prevent wrinkles, liver spots, skin cancer, premature aging of the skin, etc. Sun damage is cumulative, so the damage stays even though tans and burns fade. Some people don't even realize that suntan is damage, so they never wear sunscreen because they never burn and they think they'll be ok!
To really take care of your skin, always try to wear some form of sunscreen, even if you areen't going to the beach. You can wear a light moisturizer with an SPF like Olay Complete (I think it comes in 15 and 30) for
everyday use on your face and arms/hands and perhaps something stronger during the summer (yes, I am suggesting sunscreen in the winter

). It's very light and makes your skin feel lovely. Neutrogena makes some good 'dry-touch' sunblock (SPF 45, UVA/UVB protection, with Parsol), plus some less fancy SPF 30 oil free stuff, I believe. I tend to like the stuff that doesn't feel too slimy (oil free).
There's more on this topic on
this thread and more solutions (sunscreen suggestions, etc) on
this one.
Also...don't tan on purpose. Plese? A
slightly sunkissed look is hard to avoid if you go to the beach even with sunscreen on. I just hate it when girls turn brown and crispy on purpose to look good when they're only ruining their skin for later. By all means, get a spray-on tan if you must be leather-colored, just don't go out and fry yourself.
As for other skin care...don't pick at your skin (to avoid scarring). Moisturize plenty, drink lots of water, and wash your face regularly (but these are mostly for nice skin right now).
I hope that helps.

If you're already conscious of the sun, I don't mean to be condescending or anything. It just really is one of the best things to do for your skin.