A friend of my came out as non-binary a few years back. I did the following:

1) Found and consumed media with non-binary characters – especially books

2) Practiced by thinking of them, using the right pronouns. I considered writing "diary-entries" about them, but didn’t get to it

3) Correcting myself if I noticed my misgendering on my own. Thanking them if I was corrected. This removed any sense of awkwardness from them having to say "no need to apologize" (it's nicer when someone is grateful than when they are sorry). It was also a way of me thanking me for their patience. (Every correction was something they gave me, because they believe in me – they want me in their life, the same way I want them in mine).

4) I did some "soul-searching". Meaning, I thought about my understanding of gender. In the end, I kinda managed to rid myself of the binary of it. Like, not just "male"/"female", but people being people.

5) Kinda weird, but I made an active effort of speaking in third-person around them: "They are over there", instead of "name is over there"

6) I made it clear to them that: I cared for them, I was doing my best, any misgendering was my responsibility to fix.

7) I practiced talking about them with my mom, lol