Hey, it is admirable to offer how to teach people how to drive more efficiently. However, there are a variety of ways to drive a car efficiently. A Jeep 2001 Wrangler drives efficiently differently from a Ford F150. My good driving mantra goes...

No fast acceleration
Check tire pressure
Maintenance

Beyond that you maybe need to change the firmware in the car or...

http://www.thinkgeek.com/gadgets/electronic/72fc/

I have a realtime MPG on my Ford and it is tougher than an NVA drill instructor. I found that using the computer and altering driving habits I get nearly 35 MPG with the AWD.

If you can make money doing a class, then great. Just keep in kind that you need some concrete prrof you can deliver. This will probably require some free classes. Someone coming to me as some sort of MPG 'coach' had better deliver. Personally, I'd just suggest the above device.