Watch your speed! This can really really help your mpg.
I'm typically a bit of a lead foot, but when we moved down here to NC my friend and her bf drove our moving truck and we were in my car. Since the truck was, well a big old truck, it didn't go very fast. Probably maxed out at 65. So the whole trip down to NC I had to keep pace with them driving the truck, since I was leading. Keeping pace with them, I made it all the way from PA to NC on one tank of gas!
So now I keep my speed either at the speed limit, or just 5 miles over. (Getting a speeding ticket also helps kick you in the butt to lower your speed
haha)
And of course the usuals like you said, tire pressure. A lot of people are riding around on improperly inflated tires and they don't realize that's killing their mpg.
And don't tote around extra junk in your trunk (that sounded funny) Like for awhile I had Jimmy's seabags in my trunk while he was in CA. Then I read for every certain amount of weight of stuff in your car cuts some miles off your mpg.
Those are my suggestions! = )