Sorry about the audio quality and bg music. This was 2010 and I had no idea how to make a video back then.
Build up your ability to play fast & clean measured tremolo. When you articulate your tremolo using rest strokes, it sounds smooth and expressive. And once you can tremolo 16th and 32nd notes, it's just a matter of coordinating your left and right hands to play at really fast tempos.
This approach is based on what I learned from my teacher Evan Marshall, who showed me the importance of rest strokes. I was skeptical at first, but it's made my playing so much cleaner.
I have a remake planned for this video (with better audio quality!) where we will discuss triplet-feel tremolos, which is very common in slow bluegrass tunes, and shifting between triplet feel and 16th-feel. And we will discuss the "Brazilian tremolo", used by choro bandolim players, which is extremely expressive, fluid, and unmetered. Also, I've since realized that moving into and out of tremolo from playing single notes is a real challenge that needs to be drilled as well.
Music: "Bluegrass Signal" by John Reischmann