A - Work on your pedagogical style, your way of giving courses, how you speak to students (also by body language) ask expert counseling (use videotape).
If you're hopeless:
B - Read out loud the name list of your students in front of the audience at each beginning of a lesson, and ask them to respond to their name with the word "present".
Absences wil decrease spectacularly after two or tree times this routine.