This is the big one...
You've heard of it, but is it under your command?
It's either called I - IV - V or C - F - G or the most popular 3 chords.
Maybe you already know C, F and G but do you know that chord grouping voiced and in other keys? How about in ALL 12 keys? Now your talking!
When you can flow from one chord to the next with beautifully voiced chord notes, your playing changes forever... and it isn't hard, it just takes a little time.