Practice, Practice, Practice
Find a place where you are alone, or otherwise comfortable speaking seeming nonsense aloud to yourself (in the car, in the shower, in your home, etc) and practice the below exercises, in the order listed, out loud and as often as necessary until you feel confident in your ability to avoid offending the trans person in your life.
Exercise 1
Look at a photo of the trans person, or imagine them as you last saw them in person or in a photo/video. Focusing on their face, imagine you are speaking to them, using their correct name and pronouns.
Hello, Jamie Doe. I understand you identify as nonbinary and your pronouns are they, them, theirs.
Exercise 2
Now imagine someone else and pretend you are speaking about the trans person to this other person while the trans person is still within hearing distance of you.
Hello, Bob. Have you met my nibling (non-binary niece or nephew) Jamie? They are visiting from Oregon right now and they're working on their master's degree, for which I am so proud of them. Jamie, this is Bob, a friend of mine from work.
Exercise 3
Imagine you are having a conversation with one or more specific person(s) in your family/workplace/friend circle who are also familiar with the trans person. For this scenario, picture you are undoubtedly alone with the person(s) (in other words, that the trans person is nowhere within sight or earshot). Imagine the person(s) are accepting and using the correct pronouns and name. The goal of this exercise to use the correct name and pronouns as much as possible, even in a situation where you know the trans person is not around.
Person A: Did you see Jamie today?
You: Oh yes, their hair was too cute!
Person B: Oh, it was! And I liked their outfit, too, especially that big rainbow cape.
You: Yes, I really admire how brave they are, to wear their pride so openly in such a conservative area. I'm so proud of them and I hope they are proud of themself, too.
Exercise 4
Imagine the same scenario as Exercise 3 except this time, the other person(s) are using incorrect names and pronouns—either intentionally or unintentionally. This time, the goal is to continue using the correct name and pronouns regardless who is around and regardless whether those around you respect the trans person's identity, or consistently use their name and pronouns, too.
Person A: Did you see John today?
You: Oh yes, I saw Jamie. Their hair was too cute!
Person B: Oh it was! And I liked his outfit, too, especially that big rainbow cape.
You: Yes, I really admire how brave they are, to wear their pride so openly in such a conservative area. I'm so proud of Jamie and I hope they are proud of themself, too.
Exercise 5
Imagine a scenario in which the trans person is initially in the conversation, but leaves the area completely. While the trans person is in the conversation, have there be a time where you speak about the trans person in the third person in front of them. For this situation, imagine everyone respects the trans person's identity.
Person A: Hi Jamie!
Jamie: Hi everyone.
You: Thank you, Jamie, for joining us for breakfast. I was going to invite you to dinner, but then thought, "They really liked this diner's pancakes as a kid; I bet they'd prefer breakfast instead."
Jamie: I do! Thank you for remembering. I hope you all don't mind if I use the restroom?
You: Of course, kiddo.
Jamie leaves.
Waitress: Hi, what can I get you?
Person A: Our nibling will have pancakes.
You: Oh, and can you bring them some maple syrup? They'll want that, too.
Exercise 6
Finally, imagine the same scenario as Exercise 5, but this time, you are the only one consistently using the correct name and pronouns, and must therefore serve as a polite role model for those who are not.
Person A: Hi John!
Jamie: Hi everyone.
You: Thank you, Jamie, for joining us for breakfast. I was going to invite you to dinner, but then thought, "They really liked this diner's pancakes as a kid; I bet they'd prefer breakfast instead."
Jamie: I do! Thank you for remembering. I hope you all don't mind if I use the restroom?
You: Of course, kiddo.
Jamie leaves.
Waitress: Hi, what can I get you?
Person A: Our nephew will have pancakes.
You: Oh, and can you bring our nibling some maple syrup? They'll want that, too.