Start with a full tune up, top to bottom.

Air filter, MAF cleaning, throttle body cleaning, new PCV valve, new spark plugs and wires (AC delco 41-101), change the oil, new trans fluid with filter, proper tire pressure (35 psi is about perfect) and always always run 91+ octane gas. If you can find gas with 0% ethanol, that will normally get a 1-2 mpgs better.