The factors that have the greatest affect on fuel consumption are:
1. By far the greatest affect is the driver's driving habits: hard on the accelerator and hard on the brakes, little or no coasting up to stop lights and stop signs, consistently running up to 3,500 RPM or higher, etc.
2. Condition of the engine's fuel-feedback system: clean mass airflow sensor and correctly functioning fuel-air sensors;
3. Average cruise speed on the highway: you'll need to limit that to around 65 MPH for decent fuel economy;
4. Ratio of highway driving to stop-and-go city driving;
5. Modifications that add weight and aerodynamic drag: larger/heavier than stock tires, roof rack, roof-top tent, heavy steel skid plates, etc.
6. Tire inflation pressure: the higher the pressure, the less rolling resistance there is. The recommended tire pressure shown on the door jamb label is only applicable to the original tire type and size that the vehicle was delivered with.
7. Condition of the engine's ignition system (primarily spark plug condition).
8. The 2010 and later dual-VVTi, higher compression engines are capable of a few more MPG than the '07-'09 models with single VVTi engines.
A well-tuned, minimally-modified '07, conservatively driven, can achieve 18-19 MPG or better on the highway.
A well-tuned, minimally-modified '10 or later can achieve 20-21 MPG on the highway.
If you don't know when the last time the MAF sensor was cleaned, do it now. If the air-fuel sensors have more than about 85,000 miles on them, replace them now. Check your tire pressures. Try upshifting at 2,000 RPM for one tank of gas and see how that affects fuel consumption.