You don't mention whether it is new or used. or the year of the Sebring, but these things can be done on a used car to increase the mileage. 1.) Replace the sparkplugs, newer properly gapped sparkplugs will improve your mileage. 2.) Replace the air filter and clean the throttle body - the better the air flow your engine develops more power. 3). Make sure your tires are properly inflated and the suspension aligned - the less rolling resistance the better your mileage and your tires will last longer.