The biggest factor for me in getting higher MPG's with an HF engine was my foot. Because the engine is so under-powered, I found myself aggressively stepping on the pedal just to get up to speed. As soon as I regulated myself my MPG's got a lot better.
Proper tire pressure, stop and go driving, oil change intervals and overall maintenance are all factors, just like not tromping on the gas pedal. It all adds up, you'll get there. Just might have to change a few habits!