Remove any extra weight
Increase air pressure in tires
Replace air filter
Clean MAF (there's a how to article on this site)

Things you might have to pay someone to do
Replace spark plugs
Clean fuel injectors
Switch to synthetic lubricants

Try one at a time, monitor, try the next.

I get about 12.5 mpg on 37" tires and 3 miles to work, several more on the highway up to about 65 mph.

Wheeling a Stepside Tacoma on 37s
Exploring in a T4R Ltd V8