Have you noticed any constants with college auditions, which don’t vary from director to director?
Have you ever made any blunders (or seen blunders) that you regret (or assume the other person regrets) during an audition?
I cannot watch other's auditions, but I have seen people mess up in audition classes where they stop in the middle of their performance and run out of the room. It's embarrassing to watch.
Have you ever done something particularly impressive, which gained the attention of the director?
I think I impress directors with my improv skills. Some of my professors have told me I specifically excel in improv and should go to an improv school.
What general audition tips have you received from others in theatre, or else learned from your life experience?
Audition tips off the top of my head, I would say to be prepared and be extra prepared. Be early and don't waste their time because they want you to be what they are looking for.