Here is our standard Tuba Mirum excerpt and several pages of exercises to work on some of the challenges posed by the opening 'Call to Judgement', and the short tag that follows.
I'm not going to tell you what the exercises are working on - can you tell??
Knowing how to identify issues to be solved, and then finding ways to solve them are primary skills that need to be developed. The more creative you are with tackling this aspect of playing the instrument, the more interesting you will become as a player.