There are two major things you can do to improve your fuel mileage:
1) Inflate your tires to an optimum pressure-- this is probably somewhere between the recommended pressure (usually found on a sticker on one of the door jambs, or in the manual) and the maximum recommend on the sidewall of your tires. Doing this can lower the rolling resistance, and help you coast farther (see below) and uses less fuel to maintain a given speed.
An example of this is on my Scion xA, the recommended pressure is just 29psi, and the sidewall max is 44psi. I have found that 38-39psi is best: it coasts very well, and I don't lose any traction.
2) Drive as if you do not have any brakes. This means accelerate gently, anticipate your stops, and use one of two methods of coasting as often as possible. The first type of coasting is meant to let you coast as far as possible on as many hills and slopes as you can -- eat the "road candy"! On standard shifts, you should put the car in neutral and take your foot off the accelerator. On automatic shifts, you can also put the car into neutral and/or take your foot off the accelerator. Use your experience with familiar roads and traffic conditions to optimize your approach to stops; using your brakes only at the end of your coasting.
The second type is for when you need to stop anyway: downshift to a lower gear and use the engine to brake the vehicle. This shuts off the fuel (on most cars), so instead of wasting the energy as heat (from the brakes), you can stop using any fuel (while idling the engine and using the brakes).
For more driving tips and for other methods of conserving fuel, you can visit:
Here's a direct link to their 105
http://ecomodder.com/forum/EM-hypermili ... riving.php
As an example of how these sorts of things help your efficiency: driving my Scion xA, I have 3+ year average of just over 37mpg (EPA rates it at 30mpg Combined), and my past 90 day average is 40.1mpg, while my 3 most recent tankfuls I have averaged almost 45mpg!
Here's a thread where I show the aerodynamic mods I have used to help achieve this:
http://ecomodder.com/forum/showthread.p ... -2969.html
If you are interested, you can buy a gage for $150 that plugs into the diagnostic plug (on all vehicles after 1996), that can display all sorts of information like instant fuel mileage, coolant temperature, etc.
http://ecomodder.com/forum/showthread.p ... -2469.html
Low rolling resistance (LRR) helps mostly at lower speeds; say below 40mph. Above this, aerodynamic drag become much more significant. (Drag goes up by the SQUARE of the speed!) So, limit your highway speeds to 55mph -- this speed has almost half the drag as driving at 75mph. Go slow and steady -- and gently. Learn how to coast, and to anticipate stops -- especially in stop and go traffic: let space open up ahead of you, and gage your speed so you can avoid stopping. This will actually help the overall flow of traffic as well!
Keep track of your mileage. Pump up your tires, and practice your driving techniques to gain as much as you can from the fuel you use.