I never really thought about it, but I have five transgendered friends.
Having transgendered friends is...like having friends. Yes, that is simple but I just wanted to point that out. They all are in different places in their transitions and some I never knew any way other than the way I know them now.
There are really only two things you need to change when someone is transgendered, and that would be to never "dead name" name. You should always call them by their chosen name. Secondly, it's important to try to get their pronouns correct, but they are very understanding as long as you're giving it a shot.
What I find interesting about the national dialogue about transgenderism is, that it's almost exclusively about men transitioning to women and not women to men. This tells me that what people are really afraid of is some kind of "accidental penis incident". I know that sounds ridiculous, but how else would you describe it?
As I mentioned, three of my transgendered friends are women transitioning to men. They certainly get their share of harassment, and even though it can be very bad, I don't think it's as bad as the other way around. I kind of think all of the hate out there is tied up in some macho b.s.
I also want to mention that other than being transgendered, there's really nothing different about them. Every single one is employed, one just keeps getting promoted and another just landed an awesome gig after being spotted working somewhere else. I know that's mundane, but that's the most exciting thing I could think of to say about them. They just exist, they're just human and they just are. They don't want anything from you except acceptance and if that's not in the cards, they just want to be left alone.
You probably know someone who is transgendered or is living a hellish life because they're afraid of what you'll think. A good friend is a good friend and you shouldn't lose a friend over this. Be a decent human and just let people live.