To keep battery life up, dive into the quick settings here and be sure that the screen brightness is set to adjust automatically.
While you're here, notice these custom performance settings directly above the brightness slider, that are designed by Asus. You get a Power saving mode, Balanced, and Performance mode. These are used to throttle the CPU for better battery life, or go all-out for games. I recommend keeping the setting in the default Balanced mode until a time when you feel a real need to kick it up or down.
To see our video tutorial on how to setup an Asus Transformer Pad TF300, head over to CNET's How To blog.