I just enjoyed the honor of accompanying a talented teen in a flute contest. Here is a summary of the judge's instant feedback, a nice lesson in itself:
Never breathe during a trill. To prepare, find a place to breathe where you'll have plenty of air to do the notes leading up to and away from the trill, the alternating trill notes, the termination notes, and all the way to the end of the last note.
Trills match the tempo of the music around them, faster in fast tempos and slower in slow movements,
Nerves take the breath out of you. Flute takes a lot of breath; trills are especially inefficient. In practice, give yourself more than enough breaths so you're ready for nerves in performance or competition, and still have plenty of breath.
Tune long notes, especially octave leaps, carefully. Why do composers do that to us? It easy for anyone to hear tuning issues when the note lasts a long time.
New skills, say you've just learned double-tonguing, won't be consistent. Even so, don't give up on them, keep practicing, and use them. If you don't use it, you lose it.
Exaggerate dynamics. You are doing them, but they should be more. In a large hall, for an adjudicator who is far away, you'd need to shoot for far to much variation. Practice doing far too much dynamic variation. If you wonder if you're driving the audience crazy with your volume changes, it's probably just right.
Overall, it was a lovely performance.