First off, you don’t have to come out. There’s absolutely nothing wrong with staying in the closet, if that’s where you feel safe, particularly at high school and while still living at home. But if you’re thinking about coming out, well done! Here are some suggestions that might help:
Think about how you’re going to do it.
It’s probably going to have to be in person. Serious conversations are even more intimidating when they are in person and your parental unit might be super scary and authoritarian. As much as I wish it was easy enough to come out by text and you could just never discuss it again after that, you’re only really delaying the inevitable. Work out what you want to say.
Be aware of your audience.
You know your parental unit the best. If they’re religious, if they are aggressive liberal hippies, whatever – phrase things in ways they can understand. This is a big deal for them as well, as they might not have seen this coming.
Similarly, if you’re coming out to your friends/at school, you know them the best, and you know how to explain things. You’ll also know which one is the homophobic dildo.
People (as a general rule, although your friends/parental unit might be different) are often a lot more ready to accept coming out as the full gay, and anything else might take a bit longer for people to come around to the idea of. This sucks. Be as patient as you can.
Be prepared for the worst case scenario.
Even if your parental unit totally has gay friends, even if they were all in support of same-sex marriage, even if they seem like they’re all about this acceptance business, they might still be aghast that their child has the queer. Be ready for them to trot out tired old lines like “you’re just going through a phase”, “you just haven’t met the right man yet” and “but… grandchildren” (that last one is weirdly common).
If you’re not coming out as a lesbian/trans*, they might take more convincing because for some reason ideas that aren’t I am definitely this thing but are rather (for example) I dgaf what gender someone is when I flirt with them or sexual attraction isn’t really a thing or you know gender is a social construct well unlike the National Geographic I am not subscribing to it are just a bit more difficult for people to comprehend.
Steel yourself for the possibility that the people you are trusting enough to come out to won’t believe you, because it is much better to have a happy surprise than a bad one. Any friends who don’t accept you for who you are, are terrible friends and you should go get yourself some new ones.
Good luck, and I’m proud of you!