Tipping!

Someone clue me in here because I always seem to have trouble with tipping. Saturday I took my son to get his haircut and it was $12.00. How much should I have tipped the barber? Anyone know?

With the waitstaff at a restaurant we always tip between 15-20% is it the same when you get your haircut?

What about for women? By the time you color the gray and get it cut and blown out it could easily run $75-$100! What do you tip your stylist?