OEM spec is 35PSI - start there - I always ran 40 front and 38 rear. Fresh gear/trans fluid - new fuel filter and plugs. Clean air filter too. Drive like grandma - coast as much as you can - and avoid breaking. Roll through as many stop signs and "yellow" lights too - this will aid in the starts from a stop lol Do not use the a/c and if windows are open - ensure rears are too to improve through car airflow. Never drive with one window down @ high speeds = air trap! Buy lower rolling resistance tires (continental). Shift early - but not too soon. Install a vac gauge and watch you inches of mercury - stay out of boost as much as you can.
Are you driving an auto or manual? Highway - around town - mixed?
duct tape all the open gaps on your car so that it's one, smooth, surface. (door/hood seams, grill/bumper openings, etc). remove your side mirrors and all internal weight. Get narrower tires. (4 spare tires are the best)
In all seriousness, you're Auto in city traffic won't get the greatest milage. It's all relative though; you get better milage than any SUV.
You can also tune the ecu with more timing and some other things to increase fuel economy, most of it is in the right foot and knowing when to coast and when to shift and using only enough throttle to get you to speed as necessary,