Here are a few tips:
Only come out if it won't compromise your safety!
If you have been thinking about it for a while, and think you are ready, go for it. If you've only just discovered it for yourself, I would wait. I came out several times while I was still figuring myself out, so my parents never took me seriously.
Do a few tests to make sure they aren't homo/transphobic. Watch a show with a queer character and see how they react, and offhand ask if they'd be okay if you were like that.
I know this advice probably isn't super helpful, I'm not an expert or anything, but I can tell you my experience.
Just make sure you are safe and comfortable, and explain with facts and experiences, so they know you aren't joking and it isn't a phase.
I hope this was helpful!π
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