It depends! In my particular case, I have a verry tiny bootyhole, so I tend to be penetrated orally or stick to non-penetrative methods of sex like frotting or handjobs, or just smooching her all over. (Estrogen tends to make our skin INCREDIBLY sensitive)

That being said, if you really want to fuck a trans woman properly, I would highly recommend looking into muffing (Fingering the inguinal canals which the testes descend from or retract into) Mira Bellwether (May her memory be a blessing) wrote a fairly influential zine called "Fucking Trans Women" that goes into the subject in detail with anatomical diagrams.