I was reading an old copy of BottomLinePersonal and ran across this discussion by Richard Busse of this concept, from Fired, Laid-Off or Forced Out: After you've been warned or suspended, use the rule to develop a more positive relationship with your boss: each week, for at least three weeks, find a reason to seek out your supervisor's advice and respond positively. Recreate a positive view of you as an employee and wipe away the memory of the discipline.
Of course, if you think the discipline or behavior of your supervisor is improper or questionable, go to HR and enlist its help.