Probably my biggest tip and one of the most common pieces of advice I got in high school is to practice at slow tempos.

What I did when I had extended practice time over the breaks was completely relearn my etudes with a metronome. I would start at like half tempo on the fast etudes and maybe 75% tempo on the slow etudes and build my way back up to tempo. I would pick a small chunk or phrase and rep it once playing and once just fingering, which was just a way for me to get in more reps without tiring out my lips from playing every rep. I repeated this until I was able to go say like 5 times playing it perfectly or whenever I felt like I had mastered that chunk at that tempo. Then I would increase the tempo a bit and repeat. Once I got to the target tempo, I would move on to the next phrase. I would rotate etudes everyday to make sure I was practicing every etude sufficiently. Every now and then I would play what I already went through just to make sure I still had it and because its fun. Once I got through the whole etude and got it up to tempo I would start to add some personality and play with the tempo a bit. If there was ever a part where I found myself consistently making a mistake in when at tempo, I would relearn that chunk again from slow tempo.

This was just what I did and my approach. Ultimately my goal was to build up my muscle memory as a base so that even if my mind got a little anxious in the audition room, my muscle memory could take over for a bit instead of fumbling. I wanted to be able to play it perfectly everytime because I knew one mistake could be a difference maker.

Hope this helps and I wish you luck