Along those lines, I discovered that I had left an entire week off my otherwise detailed and carefully planned syllabus for this semester. When I first started teaching, explaining this to the class would have made me worry: would they think I didn't know what I was doing? Would they complain because now I assigned additional readings? This week, however, I went in with a new syllabus for the rest of the term, explained it briefly, and joked that although I obviously could read literature, I clearly couldn't read a calendar.
I'm thinking of other things, too, that once took a lot of time (and sometimes distress) on my part that I don't think about now:
Then: I tried to calculate when I could get them done and went short on sleep to be sure that I got them done.
Now: "When I get them done." Smile.
Then: Talk to other teachers about an appropriate penalty (rewrite? report it?), get worried, and brace myself for the discussion.
Now: Know what the penalties are. Tell the student I need to see him or her. Apply the penalties.
Then: Get angry, but don't show it. Get flustered.
Now: Give the Steely-Eyed Glare (tm). Ask the student to speak to you after class.
Then: Backpedal desperately, maybe. Worry that you don't know as much as the students.
Now: Say "I don't know. Can you tell me more about it?" or "That's amazing; I didn't know that. Can you explain that further?"
Linked to this is the knowledge that about some subjects, students will have a deep well of knowledge from some special interest they have. For example, instead of launching into an explanation of some historical or cultural event now--the Battle of the Marne, maybe, or Gettysburg, or the meaning of "elegy," or the history of the light bulb--I ask if anyone knows something about it. Often, they do, and once they've given their explanation, I can expand on it and bring it back to the class discussion.
What about you? What do you do differently now that you've taught for a while?