I know long trips can be detremental to trying to drive efficiently so either;
Keep the throttle steady
or
Use cruise control
Sure, you can do better with other driving techniques but they put A LOT of FATIGUE on you and in the long run a half ass computer can de better than a weak human mind
I (on my 266 mile commute from school to home) simply keep the throttle steady. It gains about 2-3 more mpg than with cruise control and I averge a higher speed. I have tried DWL and I get about 1-2 more mpg than with steady throttle BUT I get extremley FATIGUED!
.02