Plan your trip with your car rental if possible. If you can plan trips during the weekend, you will likely be able to rent a car for a cheaper price.
Call multiple car rental companies, or visit their websites, as soon as you figure out when you are going to be traveling. If you are traveling for less than a week, you will usually find the best deals through the larger rental companies. Ask for the rates, and also ask for a list any extra rates that could get added on. Mention the rates of competitors to see if a company is willing to match a lower price.
Call your credit card company to find out whether your card includes rental insurance. If it does, you can refuse the car rental's coverage..
Read the fine print on your contract before choosing the best deal possible. If you are concerned with anything you read, make sure you express your concerns before you sign anything.
Turn down any offer for prepaid gas. You will usually be able to save yourself some extra money by just buying your own gas and returning the car with a full tank.
Inspect the car before you leave the lot and ask the agent to note any existing damage. This way, there will no debate over whether a scratch or dent occurred while you were driving the car.