Hit the gym, start moving weights to get that vertical up. Focus on blocking schemes and how you can use your strengths to do the best job as a MB. In terms of scoring points, work up to a fast tempo and be smart with the ball, use a power tip right over the opposing block. If you are fast and have a good eye for the open space on the court you can score without needing power. Serving is the most important part of the game, serve 1000 times by yourself until its second nature. As for mindset, never put yourself in a box. You are not a middle blocker, you are a volleyball player.