The more throttle you apply the worse your gas mileage is going to be. If you want to absolutely maximize your gas mileage, use the minimum throttle possible. So accelerate only enough to just barely creep the speed upwards. On a hill, you would want a constant velocity and use terrain to your advantage. Basically put the car in neutral when going down a hill and gain all the speed you can. This will help you coast over whatever terrain comes after the downhill. On uphills, don't accelerate. Run a high gear and keep the RPM as low as possible to climb the hill.
Since you can't do these things and stay within the law, safety, and other factors, it's not clear the savings on gas is worth the hassle of driving this way.
Doing these things might change your miles per gallon by 2 or 3. Call it 2 MPG, and assume your tank has a 15 gallon capacity. You would increase your trip tank by 30 miles, and that's only for highway miles. For the city you would probably not see a 2 MPG difference. If gas costs $2.50 US per gallon, and your mileage is roughly 25 MPG, your savings is about $2.25 US per tank. Given the pain of driving like this, might not be worth it.
Hope that helps!