I've been part of the queer community for about 2 years now, and I can confidently say that the best way to be supportive is to be there for people. I have straight friends that are very supportive and will listen to all of my gay gripes. I would say the most important thing is to always be respectful and never try to intentionally misgender someone. My sister is the only person I'm out to Enby-wise, and even if she misgenders me it's not a big deal, because i know shes still supportive. If your friend ever points it out, than just apologize and make a conscious effort to use their (his?) corrects pronouns. You could even ask what his pronouns are, iif they're comfortable with it. About the crush-ish aspect? I have no idea. Maybe try talking with someone about it? Than again I've never been in a relationship, much less confessed to my crush, so don't take relationship advice from me.
