Hello mate
You should show an understanding of basic music theory, Major/minor scales, pentatonics, chord structures, cycle of 5ths possibley?
For pieces I guess its best to show some diversity, a fingerstyle piece maybe something classical or folky . Maybe a jazz piece like Giant Steps? I agree steering away from doing something by Steve Vai or Satriani everyone at those music schools tends to do them. Maybe an Eric Johnson piece would go down well, Manhattan or Cliffs of Dover?
Good Luck