If you want to control the cost of auto insurance, you must follow these simple rules:

It’s a little-known fact, but many car insurers use credit scores to help set your car insurance premium. Along with Hawaii and Massachusetts, California is one of the few states that don’t allow this practice. Generally, a lower score will mean you pay higher premiums. So if you get insurance in any of the 47 states that allow this practice, increasing your credit score and really save on costs.

A major component in calculating your auto insurance cost is how many miles you drive per year. The average American drives 12,000 miles a year, and insurance companies normally set this as the default. If you are below the average or have had a major change in the amount you commute, let your insurer know. Your reduced driving could bring your premiums down from 5 to 10 percent.

Vehicle damage is the most important factor in computing costs for auto insurers. Your premiums will almost certainly vary by the make and model of your car. If you’re in the market for a new car, ask your insurer what the different premiums would be depending on the various models you are considering.

If you add a single teenager to your auto insurance policy, you could see an average increase in your premium of 90%. This can differ from state to state, so make sure to check with your insurance on the additional cost, be flexible on shopping around, and look for better rates with different insurers.