2003 Toyota Corolla MPG very low, how to improve?

Just bought a 2003 Corolla LE. Had it completly checked with Toyota Dealer and they flushed trans fluid and installed new rear brakes and told me nothing else was required. Also they said the car is in ver good condition.

The only concern I have is that it's not giving good MPG. My first tank of gas gave 26.22 MPG. Is there couple of items I can replace that will improve the MPG? (How about oxygen sensor or perhaps PCV valve?). I would appreciate if somebody can provide a complete list of items that need replacement to improve MPG.

Thanks for your help!

Regards,

Asim Ahmed