It's best practice to ask a person about their pronouns before assuming what they are based on a person's appearance. Especially when in a group, ask everyone to share (not just those who appear to diverge from typical gender norms). Pronouns, at least for many people, are not a matter of preference but a statement of fact, so ask for "pronouns" rather than "preferred pronouns" to be inclusive. Once someone shares their pronouns, use them correctly and apologize if you make a mistake.