Here's a few:
Make sure your tire pressure is at proper spec. Low tire inflation is probably the number one cause of lower fuel economy.
Check that air filter! A nasty air filter is a restriction, which lowers volumetric efficiency, which lowers fuel economy.
A full tune-up is always a good idea, but do it because you love your car, because money spent on said tune-up takes a long time to recoup from fuel savings.
You could always save money and ride around on your scraper bike.
Scraper Bike Video