in good weather if you overinflate by 30-35%, you will see noticeable mileage improvement. just don’t drive rough on your tires - peeling out, skidding, avoid rough roads when possible, and check how the tread is doing every week. in wintertime don’t overinflate.
and anyone can use better lubricants. make sure engine air filter is replaced yearly or more if in dusty climates.
IN many cars, “overinflation” isn’t really overinflation at all, the manufacturers specifically call for underinflation of the tires to improve the “ride comfort”.
It generally is better for tires if they are run close to their stated maximum pressure (not at).
The tires on my Prius are rated at 44psi, so instead of inflating 35/33 (front/back), I do 40/38. Ride is still fine, less wear on the tires, and I get better gas mileage.
Plus, if I do forget to check them for months on end, and they deflate over time, they are still not underinflated.