You cannot tell a person's correct name or pronouns from their appearance.
Just because a person appears to be female, does not mean they identify with female pronouns. Just because a person's gender identity has changed, does not always mean their pronouns have also changed. A person identifying as a binary (male versus female) gender may not identify with the pronouns for that gender. If they have not told you their pronouns ask them.
"Excuse me, I would like to respect your gender identity. May I ask which pronouns you use?"
Until you know a person's correct pronouns, use they/them/theirs to avoid making an incorrect assumption and possibly offending them or triggering feelings of gender dysphoria.
Introduce Your Pronouns with Your Name
Whenever you introduce your name, also introduce your pronouns. This lets everyone you meet immediately identify you as a trans ally and know that you are someone with whom they can feel safe expressing their authentic selves. It also encourages people to provide their own names and pronouns without your needing to ask for them.
"Hi, my name is Arien Reed and my pronouns are he, him, his. And you?"
You can also insert your pronouns just after your name in your professional email signature.
Arien Reed, MFA
My Pronouns: he, him, his
Artist, Writer, Musician
You can also put them right after your name on a name tag.
Respect & Practice
Now that you have identified a person's correct name and pronouns, it is important to do your best to always use them. When speaking aloud, make sure you are using a respectful tone and body language. The portrayal of a negative attitude, even if unintentionally done, can cause the person to feel mocked or bullied, or to feel as though they do not belong in the current environment.
Apologize & Keep Practicing
We are all human, and humans sometimes make mistakes. When you accidentally use a wrong name or pronoun, always apologize as soon as possible (even if you don't realize your mistake until months or even years later) and promise to continue to make the effort to correct yourself.
HELLO. My name is...
he, him, his
"Alana--Oops! Sorry. Arien."
"Hey there, I'm sorry I referred to you with the wrong name and pronouns yesterday. I will keep trying to do better, I promise."
A respectful apology, even a quick one, shows you did not mean to disrespect their identity. Immediately correcting yourself, or promising to do so, also shows they matter to you enough that you will continue to make the effort on their behalf, even though you find it difficult or may not understand their identity.
Make sure you live up to your promise, and practice, practice, practice. You can ask others to point out your mistakes so you can correct and train yourself.
And remember, there is no expiration date on apologies! It can mean a lot to someone that you thought about them and valued their identity enough to apologize for your mistake even months or years after you made it. It's never too late to show you care and that you never meant to hurt anyone's feelings.