Training for the true martial artist is something you do all the time, not just on the dojo floor. It is a way of perceiving the world, and yourself. Once I readjusted my perception to view myself as I can truly become, not as I was at 16 or the grand vision of my "ultimate" self, then I found I can focus my will toward my training and not towards my negative emotions. Train as hard as you can. Train daily. Train when you are in the dojo and train just as hard mentally when you are sitting still. Train in the way that works best for you now, not then. Train, train, train. I also firmly believe that it is vital to surround yourself in an environment that engenders positive thinking. If you have found a good school then you have a great start. Hopefully you also have people in your life, perhaps a wife, who encourages and supports your journey.
This is, incidentally, my very first post. The need for a positive world about me is why I joined this forum. Thank you for giving me a place to start here. I wish you, not luck, but wisdom and perseverance toward the success I know you will find.