what can I do to help a transitioning/questioning friend

One of my male friends has just told me that he's been questioning his gender identity and is considering transitioning. Currently he still goes by he/him pronouns and hasn't had any body modifications or anything like that, it's more just (from what I can tell) he'd like to be a girl. I get the feeling he's still pretty unsure about his gender identity though. Anyway my question is how can I help a friend who's just begining to transition, who is considering transitioning or who is questioning their gender identity in general?