I honestly wish i had some advice for you, but i haven't "come out" to anyone yet. I'm bisexual and i know and accept it. I just don't have the nuts to tell anyone. That's part of my problem. I rarely let anyone get to the core of me.
anyways, when you feel it is right, just go and tell them. I've heard stories where the parents already knew or had some idea or people who were met with open arms. Speaking from the heart will help you in what you're going to say. It's hard, yes, but much of the weight is lifted off when you tell someone. As in time, i don't think there is ever a perfect time in when you can reveal something like that to your parents, but i could be wrong, because i don't have the experience.
when you do, i'd be interested in what happens, if you don't mind sharing.