If you find yourself using paper other than 8 1/2 x 11 plain, you can change the paper size by opening the drawer and moving the sensor. This will automatically detect the size of your paper.
Equally as important is the paper weight. You can change this setting by going to Paper -> Change Tray Settings -> then select your paper weight. You can the g/m² in the upper right of the screen and you can find the g/m² on your package of paper.