GHS is very complex but Adam Block summarized it very well in this video:  https://www.youtube.com/watch?v=ax9QnegDOqs

Basic First Steps:

1.  How to set a preliminary Dark point and a general overall starting point stretch:

2.  How to work with the High Brightness areas and Protect Shadows.

3,  How to work in the Shadows and Protect Bright Areas

4.  Final tweaks in PI (Saturation; Unsharp Mask; NoiseX)

He has a system...