This is very poor mileage. You need to maintain the car very well for best mileage. Replace spark plugs with new ones, replace air filter, tune the engine, replace air filter, use low viscosity fully synthetic engine oil like Zic 5w/20, change ATF with original honda oil, change power steering oil, check wheel alignment, check tire air pressure 30 or 32 psi, replace extra big tires with standard tire size maximum 195/65/15, use fuel injector cleaner regularly before every engine oil change, remove extra weight from car, replace weak shock absorbers, check free rotation of each wheel, if found any wheel feels heavy then check brake of that particular wheel.