If you keep your car in gear while coasting, your injectors turn off completely. They kick back in right at about idle rpm. I hit the clutch in just before that point. (if you're out of gear or have the clutch in, the car needs fuel to maintain idle)
Try to drive as smoothly as possible,... pretend there's a cup of coffee on your dash and you don't want to spill it. All changes in speed or direction waste energy.
I'm pretty sure shifting at as low an RPM as possible (without bogging it) helps with MPG. I sometimes shift as low as 1,500 rpm with very little throttle and take a long time to get up to speed. (I don't do that if anyone is behind me)
You have to shift at a higher rpm at speeds above about 35 mph because of the engine load needed to push through the air. (you don't want to strain your engine)
Pulling in behind a truck on the highway and drafting it can make a big difference (as long as you don't follow too close and piss the guy off).
Remember a ticket, accident or a trashed engine costs a lot more than any gas you're gonna save.
Google "hypermiling" for more ideas,... some guys get really carried away with it.