Check this link:
http://articles.moneycentral.msn.com...eIn5steps.aspx
To simplify, your credit score is a record of your debt management. You can't have a credit score if you don't have debts, so it would be good to have at least 1 credit card. To make sure the score rises, keep paying your monthly dues on time, and it is better if you pay more than the minimum. Also, try not to owe more than 50% of your credit card limit, so if your limit is $500, try not to charge more than $250 on it.
It would also be a good idea to start tracking your own credit profile through equifax.com or any of the other credit reporting agencies websites. This will help you fiind out if anybody has "stolen" your credit, this means someone may have gained access to your personal information (SS no, address, DOB) and used it to take out loans in your name.
Good luck on your first car purchase!