at your age, the pimples could be because of the hormonal changes occurring. don't need to worry about that.
just follow these advice and it should be fine.
1. wah your face 2-3 times a day with a mild soap or facewash as oily skin is more prone to pimples.
2. avoid having too oily or spicy food.
3. drink lots of water.
4. practice yoga and meditation so as to cut down on stress as stress is also a known factor in causing pimples.
and lastly, cover your face when you are in dusty environment.
if problem still persists, consult a dermatologist. he will advice a few creams or skin peeling.