Upload & Sell: On
First, thanks for the comment on my image. Luminosity masking is simply a way to selectively alter contrast and tone, so it can be called contrast masking. This may be an oversimplification, but it applies to what I'm doing with the masks.
Second, a correction. The website I linked to is not mine, it's the work of Hougaard Malan, who was inspired by Tony Kuyper. My contribution was to simply create a Photoshop action based on their work.
Having the action makes it a simple matter, relatively speaking, to experiment. The "knowing" comes from doing, seeing what works -- where and why. If most of your images seem flat to you then you should have ample material on which to practice. Run the action on all of them. If nothing else, the channel called "mids" will let you boost and sharpen (if desired) the midrange values of the images without altering the shadows and highlights. You'll also find the action is very useful for blending multiple exposures, as in my Oglebay image above.
I also recommend the demo of Color Efex Pro 4. I sometimes use it in process or as the finishing touch. Good luck and have some fun.