Through long years of experience, we have accumulated the following useful set of rules. These should be helpful to beginning research students. However, we have also observed seasoned veterans making some of these simple errors. For advanced students, these rules can also be applied to regular courses.
Always lean forward, not backward. If you lean backward your mouth will fall open and you'll snore.
Never sit back against a wall. Your head will bang against it, waking the rest of the audience. (Similar remarks apply to desks.)
Never sit on a couch. People won't like you sleeping on their shoulder. Also, couches are back against walls (see (2)). An important exception is when you are alone on the couch, in which case it is preferable to a chair. In that case you can avoid (2) by leaning to the side.
Don't bring pencil & paper. They make too much noise dropping on the floor. You might think you can work during the seminar, but you just wake up with half-written equations with long angular lines at the end. Erasers are OK.
If possible, choose a chair with padding. Plastic & metal chairs also fall noisily.
Don't bother wearing sunglasses, or asking questions right after you wake up. Who do think you're fooling?
If you wake up to laughter and everybody is staring at you, probably the speaker just referred to your work, so take it as a compliment.
Practice waking up to the sound of silence. That way you can wake up to the quiet just after the speaker finishes, and avoid being wakened by the irritating sound of applause. For you deep sleepers, this also avoids the problem of waking up in an empty seminar room. Don't think using watch alarms is clever: After the first 30 seconds of the alarm everybody will know anyway.
Don't get too much sleep the night before a seminar. You'll fall asleep in he seminar anyway, and when you wake up you'll feel sluggish from getting too much sleep. For the same reason, don't attend too many seminars in one week.
If you travel, be careful not to attend the same seminar twice. You'll sleep through exactly the same parts anyway.
Older physicists tend to sleep at exactly the same time every seminar. Try to schedule your nap to not coincide. The speaker should always have at least one listener awake at all times, especially when he finishes. Nothing is more embarassing than to wake up in a full room with no speaker.
Don't read this paper during a seminar. It will keep you awake, but the people sitting next to you will want to borrow it & you'll never see it again.
After you have obtained enough experience at this art to become an expert, you may want to apply your knowledge to more general areas: E.g., physicist parents can use seminars to replace bedtime stories.