There are no "gears" on an '04 Prius. It uses a CV transmission with no definable shift-points. All part of the technology. the best results are obtained by paying attention to the computer and energy management program. A light foot and good anticipation are great driving attributes for any vehicle if mileage over performance is the objective.
Anticipating traffic conditions and continually monitoring throttle use and using the "B" gear is best. I manage to get 4.8L/100kms by doing that. Use of the EV button is a gimmick as the battery charge is insufficient to be useful in normal commuter traffic. Done 106,600kms since 1994 and the car continues to perform to spec. Serviced strictly according to handbook by my local Toyota dealer.
*Tech note - Do not listen to this person's advice on tire psi. Never over or under fill your car tires! Fill tires to the manufacturers specs for best results... OK maybe a few psi won't hurt any thing, but filling a tire to max capacity is VERY unsafe because the tire could fail at any moment, high or low tire pressure also affects handling. The max psi on the sidewall is more for the tire tech than for you. We fill the tires up to a specific pressure in order to get the bead of the tire to seal on the wheel, we then bring the tire down to 32psi or manufacturer spec.
I was a tire guy long enough to see many damaged or exploded tires that could have been prevented by just taking care of alignment and air pressure settings.
* Personal note. My friends VW Jetta TDI gets 50mpg even though it has high miles. This car gets driven for business all over and has served him well over the years. I am not saying you should buy a Jetta TDI instead of a hybrid, I just want you all to stop and think before you buy a car. The stars make it look so cool to drive a hybrid, and you know that you feel guilty driving your 1999 Chevy Tahoe because of your green friends in the Sierra Club. Come on, be truthful, you were thinking about a Toyota Prius to make you feel good about yourself and "help" the common good. You can help the common good by mentoring a kid or cleaning up a park, or delivering a fruit basket to the elderly. Driving a car doesn't make you a hero (unless you're a volunteer fire fighter or EMT) living with morals and treating people with respect makes you a hero...
The Prius is a car, it has its place but it's not for every one - if you live in a congested city the Prius is for you, if your not a city slicker then buy a big 'ol mercury or something for all I care, but don't just buy a Prius to be "green" or "cool". The batteries will need to be disposed of some day and we will have another Eco-problem to fix. I'm sure there are more cons to the Prius, but I don't have that info so I'll shut-up for now.
I don't know about you, but I need a big vehicle to transport people and stuff. I CAN'T drive a small car because I don't fit in little cars.
I think my next car will be a Ford Explorer; the new V8 gets 21mpg and I can fit about 7 people in it with the optional 3rd row seats. The Explorer is a really nice looking vehicle too...