Powering the screen is what eats up most of the battery. Set the screen to the dimmest setting. Many phones have a light sensor that adjusts the brightness according to the ambient light. It helps, but I've found that turning off the auto and going with the dimmest possible settings really helps save some juice.
Apps or widgets that connect to social networking sites like Facebook or Twitter can be complete hogs too. They can be constantly pinging those sites for updates. You can usually adjust how often they check, or set the app to check when you start it and stop when you exit it.
4G antenna usage was one of the biggest problems for EVO users. If you're not in a strong 4G area, the phone struggles to find a good 4G connection and that eats up battery incredibly quickly. If you're not in a 4G area, turn it off.
WiFi is your friend. At home or at work, if you have a WiFi network you can use, use it. A phone constantly checks to see if it has the best cellular connection, so it's pinging towers all the time. If you use a WiFi connection, once connected, it doesn't seek another connection till you disconnect. If you're not in a WiFi area, turn it off as it will be searching for a WiFi if on and not connected.