To improve MPG, get rid of excess weight in the vehicle. Removing a roof rack, esp. its crossbars, can make a measurable diff.
When it’s time for new tires, know that there is a fair amount of variation in rolling resistance, thus MPG, among tires of the same size. Tirerack.com and every November issue of Consumer Reports have good real world data on tire performance.
Think back to your science & physics classes. Remember the law Absent applied forces, an object will remain in straight line motion at a constant speed ? That fundamental principle of physics applies to your car. Under ideal conditions you’d use no gasoline at all once you got up to speed, provided you don’t apply any force to the car; i.e. no turns or applying the brakes.
Ideal conditions impossible of course, but driving as close to that as is practical will achieve better mpg. The mpg problem w/tailgating is it requires you step on the brakes more often.
The other reason mpg is less than expected is b/c the drivetrain computer injects too much gasoline. That’s an error condition, often caused by a coolant temperature sensor problem.
Based on the car you bought, don’t consider oil changes the only maintenance item. If it has a timing belt it needs to be replaced. If it fails the engine can be ruined. Also you’ve got plugs, filters, tires, brakes etc. the amount of driving you are doing suggests these things will be in your near future and are not cheap.
No timing belt on this year RAV4 with either the I-4 or V6. If it was a Honda with a V6 there would be a timing belt.