A good and trusted friend got in touch to let me know that I had missed my intended tone on the original version of this post, so I've decided to edit it. I really didn't mean to get up on a high horse, but to provoke some thought and maybe some fresh ideas.
Basically, my point is this: we trombone players, particularly when we play orchestral excerpts for auditions, often choose to play something other than the natural, simple phrase structure of a passage, in order to accomplish or demonstrate some other aspect of what we are doing. Often, for some reason, it seems to me that we are trying to play simple phrases as if we were staggering breaths with a group of other players, in order to string together several phrases in a row and make a much longer statement.
I would like to suggest that in many cases the breathing strategy that would convey the music best and make it most logical and meaningful to the audition committee - and any other listener - would be to follow the phrase structure and breathe where it falls naturally.
Berlioz' Hungarian March is a great example. Once you get through the scale intros of the standard excerpt, you are faced with three 3-bar phrases. Many people breathe in the middle of the 2nd bar in each phrase, and then blew through into the next phrase without acknowledging the transition. I think it actually would make a tremendous amount of sense to play a complete 3-bar phrase, followed by a breath on the barline, followed by another complete 3-bar phrase, and then breathe in the middle of the third bar of the last 3-bar phrase in order to make the transition into the next set of phrases. We are consistently taught not to do that, and I can understand why - it's very easy to lose time that way, and we want to make sure the low note is long enough to speak clearly.
So, if breathing on the barlines is awkward for you, you can catch a quick breath somewhere else (I suggest the middle of the third bar of each phrase rather than the middle of the second), keep time, and still play the phrase convincingly.
I suggest deciding on a phrase structure and then practicing each phrase by itself for it's own shape. Find that shape, understand, it, convey it. Practice an entire passage with each phrase isolated. Take as much time as you need to breathe between phrases, and then start putting them together so that your sequence of phrases tells a complete story, each phrase like a perfectly structured and punctuated sentence. When you put it all back together you might need to breathe in different places, but for me it's a lot more useful to plan phrases and then figure out the breaths I need to do to to best serve those phrases.
That reminds me of the one lesson I had with J.J. Johnson...I'll write about that sometime later.