I have a 99 with a 2.2L, and a AT. I've never gotten better than 28.5mpg, and in heavy city traffic I often get under 20.
From what i've heard the AWD switch doesn't help. It also uses electricity from the alternator when you have it turned off.
The transitions are geared rather low imo. So your ideal speed may be 45 rather than 55. Drive gently, with the AT I almost never go above 2,000rpm, but that depends on traffic; safety first. I have the added motivation to do that because of an oil leak that drips on my exhaust manifold when I drive over 2K rpm.
Try to maximize DFCO mode. With a ScanGauge type tool it should be easy to get a feel for it. If you learn the point that DFCO turns off and down shift just before you can save some gas. I've found that my car doesn't go into DFCO mode at all under 35, unless I downshift. I've tried some P/N but not for a full tank so I never got a good idea if it was helping, but it didn't seem to be. Also, sometimes my brakes stop working when the car isn't running
, so I don't do that anymore, except when pulling into a parking space (with my hand on the e-brake)
It's simple to take the A/C belt off of these motors, and I gained just shy of 1mpg doing so. (my A/C didn't work, so I took the compressor out too) you might want to do that in the fall, rather than now, depending on where you live.
Then there are the things that work for all cars, many of which have been listed by others, but I will too:
tire pressure
Thin synthetic oil, trany fluid, front and rear gear box oil (I really need to do that one, it's been 40K miles...
New plugs and wire, if needed (not a big deal, that coil pack has some pep)
take off roof rack
Use the AC sparingly if at all
don't open your windows more than 1 to 2" at highway speeds
Block your radiator, or grill in the winter when your using heat
If you have any long lights on your commute turn your engine off when you know you'll be going no where for a few min. (might not be legal)
Accelerate and decelerate very gently
If you see my grandmother passing you your doing it right
Injector cleaner now and then may be good.
Good luck, Hope this helped