For the very best information specific to the prius, I have to recommend the articles at cleanmpg.
Doing a low-speed pulse&glide - pulse at 20-25 mpg up to 30 mph or so, glide down to below 10 - should get you above 100 mpg.
Once the warmup hit is past. You have to hit 157F water temp (I think), and then at a stop allow it to auto-stop the engine. After that, everything will be running in top form. It cripples some of the functions before that, in the interest of faster warmup. That's why you want to leave it powered up instead of a full shutdown for a quick stop. It'll go through the whole warmup process again, including the forced 1-minute engine-on at first startup.
