Like most faculty members, we began our academic careers with zero prior instruction on college teaching and quickly made almost every possible blunder.We've also been peer reviewers and mentors to colleagues, and that experience on top of our own early stumbling has given us a good sense of the most common mistakes college teachers make. In this column and one to follow we present our top ten list, in roughly increasing order of badness. Doing some of the things on the list may occasionally be justified, so we're not telling you to avoid all of them at all costs. We are suggesting that you avoid making a habit of any of them.