Forget taking the headrests out and that nonsense. Start aero-modding. Put a belly pan under the car to smooth the airflow. Install smooth wheel covers and a grille block. And most of all, learn how to drive efficiently. Read these through and through, then get your hands on some coroplast and get dirty!
65+ Vehicle modifications for better fuel economy - EcoModder.com
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
Here's what the underside of your car should look like when you're done:
Also try wheel skirts and maybe even an air dam. If you're clinically insane look into a Kammback!
Some inspiration in the form of my Probe:
And I believe this is MetroMPG's Metro with an aforementioned Kammback.
