Gain

Turn it up until it's loud enough, but not louder.

If loading from a template, the gains are generally set at a sane level. Some inputs with sources that change week to week (different vocalists, different guitar rigs, etc...) will more often need gain adjustment, and more consistent sources (drums, keys) will less often need adjustment.

When setting gain, place the fader around unity (0db) and adjust gain until the signal is at a healthy level in the room.

Try to avoid touching the purple gain after it is initially set, unless absolutely necessary, as it will affect everything else associated with that input. (Will change the signal level for FOH, Broadcast, Livemix-In-Ears, Recording)