Poor fuel mileage or excess consumption can be related to many conditions; engine state-of-tune, wheel alignment, brakes dragging, low tire air pressure, road, wind, and driving habits / conditions - to list only a few.

Remove the spark plugs and double-check the specific gap setting - make sure these are correct for the plug manufacturer and spark plug.

If you have access to a scanner, look through ALL your sensor readings, particularly O2 sensors, they can stick or foul and sometimes not trip a Check Engine light.

Clean the air intake, including the MAF (mass air flow) sensor, and check / replace the air intake filter - as needed.

Keep tires inflated to the correct pressure. Use the door jamb sticker recommended PSI as the minimum, and the tire sidewall pressure as maximum for the guidelines.