i came out about a month ago, and was very fortunate to have a amazingly supportive mom and the craziest, freakiest (and i say this with love)friends to back me up. i dunno if it makes any difference being a girl or a guy, gay, bi, or lesbian, but i think that you (and everyone considering coming out to their parents/family, not just you) need to know two things before you attempt coming out to your parents -
1) make sure that you have a good relationship with them and that they trust you. you wouldnt want to come out and them thinking youre playing a practical joke or sometiong stupid because they 'know' you'd do something like that.
2) if they're not ok with it, or become extremely tense around you, then you just have to let them deal with it. you can try counceling i suppose, but don't try and FORCE the fact that you're gay/lesbian/bi/whatever onto them if they're not ready to hear it. eventually, EVENTUALLY, they'll come around.
now coming out to your friends is a different story. you can always make new friends. if they want to be asses about it then FINE, let them be asses. but you only have one set of parents, and if you know they won't handle it really well, then you, and everyone who reads this that is going through the same issue, need to make sure you approach the situation carefully.
http://www.outproud.org/brochure_coming_out.html
this article helps a LOT.
good luck. :]