Encouragement: Breathe, relax, be yourself. Have you told people (friends other family members) that do accept you? This way it will not be the end of the world if it goes badly. Not saying it will hurt any less, they are your parents but still.....
Advice: I told mine in a resturant. I knew my mother wouldn't go off in public (in private she would), I played that to the hilt. If there is a way for you to control the situation to make you feel as comfortable as possible, be it environment or means of telling them use it.