During mixing, it is recommended that you leave the master fader alone, and avoid using any processing on the stereo bus. It’s mixing then mastering; don’t try to do both at the same time.
However, the master meter is still critical when mixing. Look at the meter often. Treat it the same way you would an input level during recording; strive for a good, strong level but avoid clipping.
There should be several plugins on your master channel; all to assist you in the mixing process.
High Resolution Meter
The view of the meter in the DAW is relatively small. Increase the view with a plugin like the Massey High-Resolution Meter.
Dynamic Range Meter
Dynamic range is the difference between the loudest and the softest values of the audio. The TT Dynamic Range Meter is a large meter that also displays dynamic range and RMS values.
An LED meter displays peak values useful for recording and preventing clipping. However, slower meters, like a VU meter, display average levels which are more representative of perceptual loudness. The Pro Tools PhaseScope plugin includes an RMS meter. Both the Massey High-Resolution Meter and the TT Dynamic Range Meter show RMS as well as several plugins from Waves.
A meter that displays the phase relationship of a stereo signal (i.e. left v. right). The Pro Tools PhaseScope plugin includes a correlation meter as well as the TT Dynamic Range Meter and the Flux Stereo Tool.
A phase scope is a graphical display of the relative amplitude and phase characteristics of the stereo signal. Pro Tools includes a PhaseScope plugin and the Flux Stereo Tool is also good