This is how I have been getting by. I have tried 90% of the techniques available, and probably use 50-70% of them on a daily basis. In the end the hybrids win out due to their smaller, more efficient engines and the capacity to capture energy while braking. It's also way easier to accomplish the really high-end stuff in a hybrid due to the fact that they are designed to shut down the engine on the fly at the mere lift of the driver's right foot. But the root of efficient driving is simply energy management, and that applies to every single vehicle on the road. On a good day I can see a solid 25 to 30% boost over the EPA figures (sometimes even higher.) Or, if I'm lazy, I can only do the basic stuff and still beat EPA by 10-15%.

And yes, RPM plays a role. The lower the better for the most part.