This came from Sprint today via the HTC Tutorial for the One.
Leaving Wi-Fi, Bluetooth, Mobile Hotspot, and 4G LTE on when not actively in use can drain the battery faster.
For network settings select CDMA only. (I tried this when I first got my One but didn't see a difference. But then again I do not think I was using power saver mode. The premise behind this selection is that your phone will not scan for 4G LTE.Thereby saving you battery juice. If you don't have 4G LTE in your area it's probably a good thing to use.
Stopping running applications can help conserve battery life. (Double tapping home button and closing apps that are running. This one might be debatable on this forum as to whether this helps or not.)