As a doubler on two similar horns but yet two different horns I find myself addressing fundamentals as the main point in practice sessions. I believe no matter what genre of music you're playing, fundamentals are the highest priority one should have. Personally my view has changed through the years and out of all the different parts of fundamentals I find that tone, time, dexterity, and flexibility are the most important aspects to focus on. When practicing I prioritize making my tone as pure (clear; no fuzz or air out of the corners) as possible. I feel out of the four I listed tone and time are the most important. I've equated tone with an analogy: "if you can't speak with confidence then your point will not be understood or misunderstood." If your tone isn't pure and clear to the audience will they truly appreciate what you're playing? One can make the point that tone and what's good tone is subjective but personally I feel music is about aural accessibility from sound to someones ear. Time is an important part of fundamentals as well. As a brass player our wind (air), tongue, embrochure, apeture, and finally fingers and or slide arm need to be on in sync with one another in order to make a note come out in time. Normally a sign that this is not happening would be "cracks", "fracks", or "clams" of note beginnings. If these five items are not in sync with one another then the production of sound is now compromised. I like to use analogies because my teachers always did with me. My analogy of time is when you're riding in a car and you shift out of gear because of a transmission slip/malfunction. The car is accelerating but in an unorthodox fashion. Much like playing sound is coming out of the horn but not very fluidly. Many people are respected in this art form of brass playing because of their ability to play their respective instrument with ease. This is because of their dedication to practicing tone and time.
Wrapping up, I've always been taught to use a metronome and tuner for everything. I mean everything. Scales, long tones, scale patterns, etudes, warm downs. An amazing app out right now is "Tonal Energy" and it's worth your purchase. Not only does it record you but it analyzes your intonation (tuning) and has a metronome that can be adjusted to whatever it is you're needing, i.e, 4/4, 5/4, 13/8, cut time, etc.
Hope this is something you think about in your future music endeavors!