Coming out is a big deal. It means a lifetime of hiding a core piece of their identity and finally being 100% honest about who they really are. It is simultaneously freeing and terrifying at the same time. If someone comes out to you and you are fully accepting of that person, thank you for being an ally, but please do not treat them any different than before.
The line between being supportive and being overwhelming can sometimes be unclear. Things like learning someone's preferred pronouns is perfectly fine (and encouraged). Using someone's preferred pronouns is not treating someone differently; it's acknowledging and respecting their identity.
On the other hand, things like saying, "My gay friend," every time you talk about the person is putting a spotlight in their identity when it most likely is not necessary. Coming out can be emotionally draining. Putting unnecessary emphasis on someone's identity or sexual orientation can make them feel self conscious or maybe even make them regret coming out.
Ending LGBTQ+ stereotypes starts with treating the community just like anyone else, starting with the LGBTQ+ people in your life. Yes, there might be a bit of confusion at first when it comes to how a person identifies or what pronouns they would prefer. If you are someone that has only recently become an ally to the LGBTQ+ community, you might mistakes, but that's okay. Recognize your error, apologize, and move on.
Being a part of the LGBTQ+ is not some kind of disability that needs some sort of special catering to nor is it a plea for special treatment. If someone comes out to you, that individual felt that you were important enough in their life that they want you to know who they really are. They have not changed at all, so please do not treat them any differently before.