Thank you for asking!!
Yup, asking what a person prefers works well if it isn't obvious as it's going to be different for everyone. Usually how a person presents is how they identify, but there are people for whom that is not so.

Trans and especially Transgender are pretty safe terms to use for anyone in the spectrum. Transsexual can be good, uncomfortable or sometimes inaccurate depending on the person. Tranny, he-she, she-male and any others that are similar are no good. Basically stick to trans or transgender if you need to use the terms. But for the most part, just treat any transwoman like a girl or woman or any transman like a man or guy and non-binaries like any person and you are good to go! That's kind of what I've gathered, anyway. Someone else might have other suggestions.