Upgrade your fuel filter, air filter, spark plugs, and plug wires. The ones they stick on at the factory work, but don't provide optimal fuel consumption. Doing this, and watching my tach I got an old Forester to get around 25mpg delivering food.

maybe make sure injectors are working properly (defective injectors have more fuel return thus higher consumption) ? or throttle body uncalibrated ? or good fuel pump motor. After changing the fuel pump motor i had a diesel mpg (60mpg) with my gasoline car (which used to be at 30, sometimes 20mpg, which was too much :/)