Gain staging is a fundamental and simple concept that often is misunderstood. A proper gain staging allows you disparate things: having headroom enough to don't clip on your master channel; don't clip the plug-ins, and using analog gears (or analog gear emulations) at their sweet spot.
Doesn't it sound good? Well, you have to know that a well-managed gain staging can radically improve your mix.
Gain Staging 1 - No distortion on your master bus
To make sure you don't clip on your master bus start your mix at a relatively low level. Starting with the kick at -14dBFS usually works very well. If you are working at 24bits, there won't be any loss of quality.
Gain Staging 2 - Don't clip your plug-ins
Make sure none of your plug-ins is clipping at any stage.
Clipping introduces digital distortion and harshness... this is something we want to avoid
Gain Staging 3 - Analog gear and analog emulations
On plug-ins that emulate analog gears, you often find a VU meter. With these plug-ins, try to work around 0dBVU. This value indicates the sweet spot of that unit. Usually, these plug-ins have an input and out knob that you can use to adjust the level if you find your signal being too soft or too hot (same application for analog gears).
Extra tip: sometimes is worth trying to drive harder these plug-ins or analog gears adding extra saturation.
Gain Staging 4 - Read the manual
Don't underestimate this resource of info.
It comes with a plug-in, and it can give you valuable info on how to use the plug-in at its best.