The Online Photographer has a very useful essay on how to actually succeed at that New Year's goal you may have set to hone your photographic chops. The gist:
Set mechanical goals. That is, goals of time, number, frequency, or duration. Photography is a game of doing, and things get done only when you get going and do them. ....
...Leave the elusive parts of success to work themselves out. Plain, literal goals can be met more easily—all it takes is things you can control like dedication and discipline, not the more ephemeral things you can't control like talent or luck or weather or opportunity, or things coming together in that semi-magical way the way they sometimes do.
This approach echoes the focus of Outliers: The Story of Success, Malcolm Gladwell's book, in which he argues that it takes literally about 10,000 hours of practice to master a skill. A lot of that time is simply spent building the muscle memory to embed a perfect pitch, sonata, or whatever into your automatic responses.
For photographers, an obvious—and bedeviling—example is knowing exactly which camera controls to change in which circumstances. Maybe you'd be better off sticking with a particular camera for several years instead of trading up every 18 months. (After a lifetime of Nikons, I'm having to relearn that my Canon S95's aperture ring moves in the opposite direction.)
How you go about applying this same approach to Lightroom? Take your big goal (the outcome) of mastering Lightroom, and break it into concrete chunks of practice (the process).
Want to know how to work the Tone Curve to best advantage? Use it on every photo for a week or two or three, and ease up on using the sliders in the Basic panel. Ditto on the Luminance panel, and right on down the line. Process and practice are the little steps to get you to that eventual goal.