Come to class ready to learn. Turn off the cell phone,. Do not leave your cell phone on vibrate; it is still a disruption to the class. Be sure that you have gone to the bathroom, gotten something to eat, and have all your necessary books, pens, and paper. You should not be getting up and leaving in the middle of class on a regular basis, even just to make a phone call. Save those types of behaviors for an emergency.
Learn your lecturer, by knowing his or her habits you can avoid trouble