Maintain a good driving record. Insurance companies reward drivers who aren't accident-prone and who obey traffic laws.
Check to see if any professional or social organizations you belong to offer group discounts for members. Groups like AARP offer discounted rates to members.
Maintain a good credit record. Your credit history figures into your insurance score, the way insurers rate you as a potential customer. A good insurance score will get you a lower rate.
Raise your deductible. One of the easiest ways to lower your premium is to be willing to absorb more of the cost of any damages.
Get quotes from more than one type of insurance company. That means checking out online-only firms and firms that don't have individual agents as well as the name-brand companies with offices just down the street. Find the best offer, and tell the other companies you call that you have this other offer. Ask them to beat it.
Ask your insurance company for a better offer. If they can't beat the rate, ask them if they can throw in extras like roadside assistance or a free rental after an accident.
Get a quote, and then work on improving your credit score or your driving record. If you can hold off on acquiring the policy for a couple months, you can possibly get a better deal by improving your record. This, of course, does not work if you don't currently hold insurance and are required to by law.