[aussie muscle]

Weight: don't carry anything in your car that you don't need. it all adds up and costs you in extra fuel if you're carting a lot of 'junk' around with you.

Style: Smooth acceleration and braking is also important. The more you brake, the more fuel you have to use to get back up to speed.

Coasting (zero throttle) from when you see a lower speed limit can also help, instead of driving at speed right up to the signpost (most drivers seem to brake at the last second).