It was just brute force. I worked every evening, every weekend, on the tube on the way to and from the office. During my lunch hours. My coworkers knew not to interrupt me during lunch, because I always took a sandwich to the same desk, put my headphones on, and worked. Have you seen that comic "You must burn", that's exactly it. It's painful, there's moments of crippling self doubt, there's moments when you'd rather…
Expect to fail. And while it shouldn't be a goal, my failures have always been more beneficial, more productive than any success. Success always has the risk of promoting complacency. Failure will test your character and grit. In the end you will know more about yourself having tried than not. I also recommend doing it as young as possible. It helps to teach you the possibilities. If you decide it's not for you then you have time to start over and rebuild. Maybe with maturity and a different perspective you have the opportunity to pursue it again later on.