Start by hearing, believing, and listening to your patient. Trans people are no different from cis people in their medical needs, they just need their hormone profile bringing into line with their correct gender identity.
First, make sure that you are respectful with your terminology. Ask the patient for their name, pronouns, and gender identity. Each person may have terminology that is specific to their own experience, so allowing them to use their own language is the most respectful method.
Get to know your trans patient by asking them about their gender journey. How long have they felt this way? How did they come to understand themselves and their gender? When did they start to disclose their experience with others? In the case of younger patients, ask if they have discussed this with their parents/guardians, and if not, whether they would like to have that conversation together.