Steam clean your interior
As Top Gear proved ages ago, your car is a rolling hazmat scene. You sweat in the seats during the summer, drop particles of food and spill small amounts of beverages, and perform any number of disgusting personal habits while sitting in your car that you don't want anyone realizing you do. If you're not your car's original owner, just try not to think about it on your way home from work today, while your car's vents blow God knows what in your face.
You should really do this more often, but at a minimum of once a year, take a steam cleaner and blast away all the germs and miscellaneous bodily fluids. It's not going to hurt your leather, faux leather, vinyl, or fabric seats, and it's definitely going to make your car more clean/less biohazard-y.