the first thing is to check for things like low tire pressure, bad alignment, dragging calipers, wheel bearings, and clogged filters like mentioned above.
If your commute is stop and go, or has hills with lower speed limits that don't allow coasting, then your economy will suffer. I can get 28mpg on fairly level road at 49-53 mph. It drops dramatically at speeds below that since you're driving around in 4th gear. You should still be able to get 24mpg at around 70mph, but faster than that, it will drop quick since you have to overcome drag.
The best thing you can do to help economy, and safety, is to anticipate whats happening ahead of you. Ease on and off the throttle a little more progressively and try to coast as much as you can. Maintain enough distance to the car in front of you so as they stop, you can just coast up. Just remember that every time you hit the brakes, you are wasting energy.