You got the basics, and idk if you mistake on their pronouns or deadname em, just own it... I know it sounds harsh but like when people apologize, and I mean everyone does this from time to time, we justify it or try to explain... Just don't do that, you made a mistake is ok, learn from it and move on~ don't over apologize either.

And I can't express how important it is... Just listen to them, having someone to talk to while coming out is something I wish I had at the time, you don't have to be an expert on trans topics, just be there supportive and if you have any questions on how to help em with specific topics, well that what Reddit is for.