Here are some of the things I did to practice and work on these skills when i student taught and I'll still do these today as an assistant during the Head director's band class.
1) Bring sticky notes or a notebook and write after each run, exercise, section work etc. write down the gist of what they worked on (Ex: "Book pg 4 #1" or "In the shining M 25 brass") then after each run write a comment you'd say to the group, something quick and simple. Find SOMETHING even if you put "entrance not together"
Then you listen to what your mentor teacher says after the run. Write THIS down next to or below your answer to the run/section. If your mentor teacher says the same thing you did, draw a shape (I like stars) congrats you get a point. Your goal is by the end of this semester to obtain 70% of the total phrase points for every single class that you assist teaching in. Then in your first year of teaching do the same thing with head director's, region band clinics, etc. This will help train your ears
2) Another technique you should get acquainted with is score study of each piece, as you look at each piece (INCLUDING lines in a beginner book) you can tell by looking at it the general things bands will get wrong. create a list of these. (If you don't know ask your middle school teacher mentor especially since younger kids are more consistent in things wrong) then you can check for these things marked in your score as you run through sections and areas.
sorry for the block of text, I hope this is helpful to you!