I agree with the above except for the following:
Poor Man's Hybrid - You will wear your starter out doing that. I did. I wore mine out at about 140,000 miles on the Saturn. I'm sure it would have lasted a lot longer. Of course, I only spent 200 bucks on installing the rebuilt starter.
Windows Up - A friend of mine did a test at 55, 60, 65 and 70 mph. The largest mileage losses were from using A/C versus rolling the windows down at these speeds in his 2006 Kia Sportage V6. AC is a fuel guzzler. The car lost 3-4 mpg using AC. I use my A/C sparingly, although not sparingly enough.
As for driving slowly, forget about it. I can't hold a car to 70 mph on a rural interstate.