Wendy, Prius drivers found that they get their best mileage doing something called "pulse and glide". If you do a search you'll find much info on it. In this method you accelerate reasonably quickly to about 40 - 42 mph (pulse) and then let off the throttle to allow the ICE to shut down. You then feather the accelerator so that there's no energy transfer showing on the MFD, or the NAV display if so equipped (glide). If you give it too little throttle you'll see regen (energy transfer from wheels to battery) and if you give it too much you'll see the motors driving the wheels (energy transfer from battery to wheels). You stay in this glide until your speed drops to about 30 mph and repeat the process. This allows the ICE to be used for a very short while to propel the car while glide allows for going the furthest with the ICE off without reducing your SOC.

Some people on this board (XCEL I believe) had a run that was covered in magazines of over 100 mpg with a Prius over a full tank of gas. I tried it in the TCH for brief periods. It gets very high mileage, but it's not fun.