In my own personal practice, something that I have always found extremely helpful is hearing things specific to my own needs. It is true, we as your band teachers cannot focus on individuals during a normal school rehearsal. SO ~ It is important that you learn about what things will help you become better ON YOUR OWN. Private lessons are a great start. If you can't do that, at least spend some time learning about playing the trumpet, horn, trombone, euphonium, or tuba BETTER. The band gets better when EVERY INDIVIDUAL improves. DAILY.
The following are some videos that will help YOU learn about what YOU can do to help YOURSELF play better.
For Euphonium and Tuba