Drive about 40 - 50 m.p.h. is best as far as wind resistance goes. But keep the vehicle in top gear.
Drive as though you have raw egg between your foot and the throttle - no jack rabbit starts, please!
Try to avoid braking as much as possible, for braking means that you used too much gas just before that. Driving aware of what's going on ahead means that you'll take your foot off of the throttle sooner, when there's congestion ahead.
Drive between 1/8 - 1/4 mile ahead of you, keep an eye on what's going on along the edge of the road, and in the rear-view mirror.
That's safer, as well.
When you see a traffic light go yellow half a block ahead, if you're driving an automatic, take foot off throttle, your choice as to whether to shift to neutral (at speed, it'll slow you down). You'll get to know when it's wise to do that.
I drive a standard tranny, and I push in clutch, turn off ignition. When it's a light with whose cycling time I'm familiar, I try to arrange to be 100 - 150 feet behind the last car in line at the time that the light goes green, depending on speed that I'm travelling, a bit farther if there are more than 3 - 4 cars ahead of me ... which means that I usually arrive at proper space behind the vehicle ahead when that driver gets up to speed. Then I turn on ignition key, let out clutch, starting the engine again. Uses much less gas than starting from standing still.
Some years ago I drove 20 km. (about 12 miles) daily to Uncle's farm to look after the house after his death, usually late at night, when there was little traffic. I found that, when I got to know all of the little hills and vallies, I could turn off the ignition and coast for over 80% of that journey. Which I did not do, of course, if there was a vehicle following me.
But that was the wrong approach. As I'd often start the engine in third gear (instead of fifth) and push the engine hard when going up a slight grade, prior to the next downhill slope.
The optimum method would be to keep the car in fifth, and run the engine or stop it as required, but not to push it hard, as that uses much more gas than gentle throttle.
It's not the number of kilometres/ miles that one coasts, but the amount of fuel used that's the important issue.
Let's walk with a gentle footprint on this precious earth. We've been pillaging our resources for a couple of generations.
The people of the third world have a point when they say that they should have a right to use more energy than they have been, in order to improve their lives and that we should cut back, for we've been wasteful.
Should we tell others that they don't have a right to have a fridge ... or a car?
Not quite fair, is that?
In the meantime, the ice on the Arctic ocean is thinner and dark water that absorbs more sunlight is present for longer periods in summer.
And our glaciers are shrinking. When they're gone, the important rivers on our prairies, that are short of water now, will have a much lower flow.
New Orleans had better build higher levees, when they rebuild.
And some others cities built near the oceans, as well.