[Ecky]

What instrumentation do you have? Generally, the largest improvement comes from having driver feedback.

Do you use the garage's fuel log? Data is useful, and by logging your tanks, you can get an better idea of how weather, conditions and modifications affect your averages.

A lot of methods being recommended here are tested and proven. I understand that you may be skeptical of some of them, but the data is here if you want to know.

I understand you're not, you're just looking for ideas, but if you have a difference in opinion about something and would like to recommend it for others to try, having data to back up your assertions lends credence. I hope I don't come off as harsh, but I'm highly skeptical of (as an example) running exotic fuels and doing 6-8x as many oil changes as a method of saving money over time.