I try never to be late. Of course, I miserably fail. I am a sleepy head and a woman after all. ;)
When I am late, I try not to make excuses. I am just honest. Of course, sometimes it's just "I overslept" or "I got lost on the way here". Those are embarrassing. Forcing myself to semi-embarrass myself because I am late, I automatically teach myself a lesson and will keep that in mind for the next time - and be on time instead.