Here's How:
1. Find out the age requirement. Some companies will not rent to people under 25. For others, the minimum age is 21.
2. Compare prices online at multiple online travel agents. You may find rates vary from day to day, so if you have the time and inclination, be patient and check prices several different times. Know that the price will go higher; steep taxes, insurance, drop-off charges, and filling the tank all add to the bottom line. You may be able to find a cheaper rate with a local company, but the cars may not be as new.
3. Determine if you are entitled to a free upgrade or discounted rate. Ask the boss if there's a corporate discount available to you. Do you belong to the American Automobile Association (AAA)? Membership costs less than $50 and yields discounts on car rentals and hotels. Car rental rates in the same destination may differ, depending on whether you pick up the rental car in the city, at your hotel, or at the airport. Off-airport locations with free shuttles can help you stay within budget.
4. Understand that car classes are represented by different marques at different car rental agencies. For example, "Luxury" at Budget may mean a Lincoln Town Car. At Advantage Rent A Car, it can mean a Chrysler Pacifica. And at Hertz, it's often a Cadillac Deville. Don't expect even a top of the line rental to have the same bells and whistles, such as lumbar support or heated seats, as a privately owned one. Rental cars are typically base models.
5. Book early, especially if you're going to a popular place during peak travel time. Ask if there's a drop-off fee for leaving the car at a different location than where you picked it up.
6. Ask what the cancellation policy is before you provide your credit card number.
7. Only rent what you need. Don't pay for a DVD player or GPS navigational system unless it's a GUI, in-dash unit that you will use. The same goes for satellite radio.
8. Don't pay double for car insurance: Acquaint yourself with the coverage provided by your credit card company or insurance agency.
9. If you're not legally married and both of you plan to drive, make sure both drivers' names are on the agreement.
10. Don't accept the option of returning the car empty. Fill up on gas before you return so that you aren't charged a premium when the rental company refills the tank.
11. Inspect the car before you pull out of the agency parking lot. If there are scratches, dents, broken lights or anything you believe to be unsafe, report it.
12. Ask for a free map and directions. Check out the location of speed traps along your route beforehand.
13. If you plan to be a frequent renter, join a rental agency's membership club to take advantage of special offers and quick check-in/check-out.

Tips:
1. Ask how much it costs per per day to upgrade to a higher-class rental car. The cost can be quite affordable -- and a lot more comfortable.
2. Familarize yourself with the car's lights, windshield wipers, and radio before you pull out of the parking lot.
3. On a long drive, bring along favorite CDs, audiobooks on cassette or CD, or iTrip with your iPod.
4 .Yes, convertibles are fun. But they're also more dangerous than sedans, noisy, and require frequent applications of SPF.
5. Leave enough time before your flight departs to return the car.

What You Need:
Driver's License
Full Tank
Directions to Your Destination