Adjust screen brightness
Adjusting your screen brightness is one great method on helping to manage your battery life. Keeping your screen at a high brightness will drain your battery quicker, so it would behoove you to only keep the screen only as bright as you need it, and no more. To adjust the screen brightness, simply open the "Screen & Lock" app and drag the Brightness slider to your desired level. You can also specify the length of inactivity of the phone before the screen will automatically turn off.
It's also important to note that the keyboard brightness of your device is directly linked to the screen brightness. As a result, if you put your screen brightness too low, you will effectively turn off the backlight of the keyboard. If this is not your desired behavior for the keyboard brightness, there are a number of patches in Preware that will keep the keyboard at a fixed brightness, or the "Inverted keyboard brightness" patch will invert the relationship between the screen and keyboard brightness, so the lower the screen brightness, the brighter the keyboard becomes. Another options is to install the Homebrew app Brightness Unlinked that will give you separate sliders for the screen and keyboard settings.
Finally, you may also want to consider installing one of the many "Device Menu" patches that will put a Screen Brightness slider directly in the menu when you swipe-down from the top-right of the screen. This way, you can adjust the screen brightness from almost anywhere in webOS with just a simple swipe-down gesture!