| No matter what your age, a great credit record really comes after being given a sizeable loan like a car loan or home loan and making payments on it regularly. A credit card alone won't improve your FICO score that much...it is better than nothing.
At your age, if you want a good FICO score, you could have your name added to your parents' credit card account. This way you kinda inherit their credit score. Of course, the catch is, your parents must have good credit and you should not abuse that credit card.
By the way, there are ways that your FICO score will go down (besides the obvious way of not paying your monthly loan or credit card payments). For example, multiple credit checks in a year, canceling credit cards, and opening too many credit cards in a short period of time.
(For more information, check out Suze Orman. She's great for all of this kind of basic financial questions.) | 
