Although making all of your payments on time is a big factor when it comes to building your credit score quickly, there is more to it than just that. Keeping your credit card balances low and not applying for more credit will also help get your score back on track. You should also keep all of your old credit cards open because closing a line of credit can negatively affect your score.
If you need a car now, there may be lenders that are willing to work with your bad credit. Although the interest rate on a bad-credit loan can be high, refinancing is usually an option after six to 12 months of on-time payments.