practice and observation
I want to get better at speycasting. I need to know how I'm currently doing and what aspects of my casting to pay attention to next. Those are exactly what I don't know. To make rapid progress I need the help of another person - someone who is both an expert at speycasting and also an expert at teaching speycasting. In my case that person is Gary Scott (who took this short video).
I've no doubt there are masses of faults in my casting technique. That's irrelevant and not helpful and does not deter me at all. What counts is working towards some improvement in the next video.