Hi,
I would assume that you are in your adolescence period. First of all, you need to know that acne or pimples are NOT caused by fried food or chocolates as we commonly believe. However, there are skeptical reports that certain food still are the culprits behind acne. If you choose to believe this, watch your diet then. Afterall you are what you eat.
Acne is caused by your your hormonal changes happening inside your body, and is very common during puberty period. Most likely you have an oily complexion. Sebum is an thin layer of oily substance naturally produced by our face for protection against dirt and other stuffs. However, during puberty, most pple can over secrete sebum which in turn traps dirts, though NOT directly related to acne, but an inhibiting factor for acnes to surface.
Here a few pointers:
1) Wash your face at least once a day, but never overwash your face. (Remember the sebum?)
2) Never over-scrub too. It actually do more harm to your skin than you think.
3) Drink more water. Don't underestimate the healing power of water. Afterall 70% of our body is made up of water.
4) If you are a lady, wash your makeup thoroughly before going to bed.
5) Use "oil-free" cleansing products, say Clearisl or Neutrogena.
6) Ask a pharmacist about your skin condition, remember not ALL products are good for your skin. If your skin is sensitive, harsh cleansing products can actually make your acne even worse!
7) Avoid direct sunlight.

Have enough rest = beauty sleep. Skin is a living material, they need rest too.
9) If you have long hair that touches your forehead, wash it everyday.
10) Prevention is better than cure. If you don't take care, in serious cases, acne will leave scar marks on your face. Not a very good sight.
11) If you apply hairspray or gel, cover your face while doing it. Those products can irritate your skin.
Lastly, if you really need help, go th National Skin Centre. They can help you, but the treatment can be expensive, depending on your situation.