He's late for work, acts brusque, and seems sullen. One morning he walks into the office, knocks over a pile of paper, and leaves it lying on the floor. We'll use your answers as part of today's lecture. The correct answer is alcohol. Vary your opening.
Any dramatic technique loses impact upon repetition.
Announce the objectives for the class. Tell your students what you expect to accomplish during the class, or list your objectives on the board. Place the day's lecture in context by linking it to material from earlier sessions. Establish rapport with your students. Warmth and rapport have a positive effect on any audience.