First of all, you should know your specific state's requirements for general auto insurance coverage. Each state has a different law, so knowing yours will be important. However, you shouldn't limit yourself to only purchasing the amount of auto insurance coverage that you need. Instead, you should purchase enough coverage so that you are financially secure. That is, after all, what auto insurance is designed for.
You need to understand the different types of coverage available as well. The differences between liability coverage, comprehensive coverage, and personal injury protection are simple to understand, and informing yourself will help you to better understand what you're paying for. For example, bodily injury liability coverage pays for injuries for yourself and others on a per person or per accident basis. Comprehensive coverage pays for all non-accident related expenses, such as theft, natural disaster, or fire and water damage. If you spend ten minutes to know these terms, you'll be a more effective auto insurance shopper, and should be able to find cheaper rates.
You should also know the importance of shopping around for general auto insurance rates. Many companies offer similar rates, but by getting multiple quotes, you're giving yourself more options for insurance. You should never purchase the first policy that you get a quote for, at least not without checking out a few other policies. Also, you shouldn't choose a policy just because the cost is low, or because it's the most expensive. Price is relative to the coverage you get, and needs to be compared as such when you are shopping for general auto insurance.