Stop giving zeroes for assignments, awarding bonus points for non-content, increasing grades as part of class "curves," providing extra credit to "help" grades, and all other practices that distort or misreport a student's level of mastery.  Effective teachers know that grades should reflect mastery.  They also know that it's better to barter behavior with privileges, not points.  Grade inflation, reduced student effort, and academic misconduct have reached epidemic levels in our society.  Be a part of the solution and not the problem.