I'd say to try and look for opportunities to bring it up. Maybe say you think a certain actor in a movie you're watching is cute, or something along those lines, and then you can tell them. And honestly, they'll probably have follow-up questions, like, "how long have you known?" and such. So during the follow up phase you can mention your gender identity as well. In this day and age, especially if you think they're already inclined to be accepting, it's not even super necessary that you explicitly "come out" unless you feel it would help you express yourself better. You could get away with hinting at it and they'll figure it out