How can I get my band teacher to give me a good recommendation?

For the school I want to go to, I need a recommendation from an arts teacher, as I'm applying for a performing arts school. The only arts teacher I have is my band teacher. I haven't been the best band student and I have 3 or 4 months into the school year to convince my band teacher that I have changed and practice a lot and am dedicated to the arts. I also have to show him that I am very dedicated to theatre and find people with the same interests as I do. We have morning ensemble programs, so I plan on joining one of those, as he always pressures us to join them to help us improve. In the morning, we have rooms available for practicing, so I am going to practice in the mornings so he can see me come in and practice. What else can I do to show him that I have changed and am dedicated? Also, can you give me French horn warm-ups if you have them?