I suggest a riding school. I went to a trackday first and realized that I needed more extensive training than what I learned at a trackday. I've gone to a riding school multiple times since then, and now I'm a completely different rider. I've watched riding videos and read some stuff online, but nothing quite compares to being coached while riding. I am a hands-on learner, so your results may vary. Actually, at the end of my most recent riding school class, my coach was stunned and told me that I was a completely different rider just from the morning to afternoon.