Since I'm just starting to learn euphonium, I found this resource to be really valuable in giving me a source for music to practice with for sight reading and learning parts I may be playing once I join a local community band. When I have some time, I'll watch that video, for sure. I'm sure I'll be playing different arrangements later, but these parts are extremely useful to me.
I've also found many resources by searching for audition excerpts for euphonium. Different organizations publish excerpts in PDF format for auditioners to practice, and those are also good sources for practice material. I'm operating on a tight budget, so I haven't purchased a lot of material yet. At my current stage, I'm spending most of my time learning and playing scales and working on tone production, articulation and intonation, but I try to read through something during each practice session, too. It's often a bit ugly and slow, but excerpts are still helpful to me, even at this early stage.
Practice sessions are still relatively short for me, as I build embouchure strength, and I'm stopping when muscle fatigue begins to affect tone production, so it's two shorter sessions each day for now. I'm hoping those sessions keep getting longer and longer, though, as I build endurance. It's all an interesting process for this old woodwind player.
3-valve Blessing B-350 Euphonium