The old joke about how you get to Carnegie Hall has been around a long time, but the question is; how? There is and should be, many ways of practicing and with many goals in mind. Simple maintenance, meaning keeping in shape what you already have. This means not advancing any improvement in all the things that go into playing in an exceptional manner. Another way is picking out a particular aspect of playing and focusing completely on that one thing, such as sound, technique, legato, articulation etc. This type of practice will probably not affect endurance, or keeping in shape because it is centered on one thing and will require repeated trial and error, and therefore lots of stopping and starting, which will not increase endurance or “keeping in shape.”
The most important question a player must ask themselves is; what ever facet of playing someone is working on, “can I get a better result?” This sounds simple, but I believe the biggest mistake students make nowadays is only “covering material.” Playing lots of notes with the same approach and result, and thinking somehow that that alone will make someone a better player. Actually that approach will only “groove” the level already attained, and actually inhibit possible improvement.
Your practice room is your R & D laboratory. That means constantly questioning the quality of the product and finding flaws and ways to improve those flaws. Some of the things I’ve tried in my practice room I wouldn’t want the world to hear, but thats what a practice room is for. For instance, working on dynamic ranges in excerpts; playing fortissimo excerpts much too loud and pianissimo excerpts much too soft in order to have a margin of safety in public. I wouldn’t want that practice to be heard in public but it’s important in my laboratory to go into unchartered waters to find out what the possibilities are.
That brings me to a very important point which I have delved into before but which bears repeating: in order to find out where the optimum point for an aspect of playing is, you must go beyond that point, or “cross the line.” This can apply to just about everything that goes into playing an instrument; dynamics, vibrato, legato, registers, articulation, etc. Example; when someone has a hard, jerky legato, which is the most common fault I find in today’s world, I’ll have them not stop the slide in any particular position, but pass by each legato note while keeping the air flowing. This has a wondrous effect on wedding the air stream to the slide movement. Then when I tell them to stop in each position but mentally pass by as before, the sound and legato markedly improve and the incidents of “blanks” (yuck!) is practically eliminated.
Generally speaking, if you want to be comfortable in the high register, practice in that register even if at first it sounds bad. The same for the low register. The most neglected register in both tenor and bass trombone pedagogy is the one between low Bb and middle F in the bass clef staff. For some reason both instruments would rather concentrate on other parts of the range. The reality is, much of the literature for both are centered in that space, so it is important that much time is spent becoming comfortable, meaning clear and focused in that range. The Arban method deals principally with that register, which is why it may be the best complete method ever composed. I remember years ago spending an inordinate amount of time in the Arban book in that register, and noticing that it helped both high and low registers (without going into them) and putting me in some of the best shape I’ve ever been in. Go figure?