Start by making sure all of your current bills get paid on time. If you have any outstanding debts, get those paid. Avoid at all costs applying for credit cards. You know the kind, you walk into the store and someone offers you a 2 liter of soda, or 5% off your shopping bill if you apply.
Keep you car insurance paid (this is very important because they are running credit checks). Try to prevent anyone from running a credit check at all. These show up on the 3 major credit bureaus.
If you must have one credit card, that is fine. Keep your total available credit at a low of $200 if at all possible and then, don't use it. If you must use it, pay it off by months end.
After that, once your credit starts getting good, if you should find the need to get a loan or credit of any kind, you interest rate should be a bit lower.
Lenders charge a higher interest rate for a lower credit score.
Hope this helps!