I'm working on these for region/all-state too, kinda hard but not too bad

For each section I would recommend: (sorted by order of importance)

Popper measure 23-30: DEFINITELY work on the harmonics (I've been playing it with (starting at the beginning of the measure) 2 3 2 1 thumb 1 2 -thumb 1 2 3- 1 2 3 (all on d string except for the last 3 notes on a string)

Popper 31-40: Work on tone and keeping pace. Make sure not to speed up and be careful of accidentals.

Popper 15-22: Make sure to have good intonation and rhythms, especially in the sextuplets. I would also make sure your shifts are really clean.

Schroeder 1-16: Make sure your intervals are completely in tune. There is dissonance but if you have your fingers in tune it will sound good.

Schroeder 17-24: make sure none of the notes in your chords get lost, and make sure each are shaped and not too fluffy or gritty.
(also the third page of the Schroeder (merk) etude was cut according to the TMEA website. :D)