The tip for today may not be feasible for everyone. It certainly is not for me at this time. However, if the cost is worth it, this may be the best tip of all:
Buy a Hybrid.
Many people, though, see "55 mpg," go out and get themselves into major car debt. Hybrids are not cheap. However, if you are going to use the car primarily for city driving (stop and go), and you can get a nice used hybrid at a decent price...and can pay cash for it...then this tip may save you a ton of money.
To help you do some research, here is a link to hybridcars.com. While, obviously, they are trying to get you to purchase a hybrid, the site is still good for a starting point in your research.
Also, it's not too far in the future that we will see cars that are all electric. In fact, Chevrolet is coming out with the Volt, possibly by the end of the year. Here is some information on that car.