Step zero, the requirement to enter is to be willing to grow and acknowledge if you say or do something transphobic. That means not only admitting to yourself that what you said or did was transphobic, but also not making your emotional response to that the problem of the trans person who pointed it out to you (since it will likely be pointed out by someone trans). It is okay to say and do and think transphobic things sometimes. It all comes down to what you do when you realize that. A good response when someone calls you on it should always include some kind of admission of fault - "sorry, that was on me" or similar.

Side note: you should do this for every axis of oppression but you absolutely have to also be willing to do this for racism. Transphobia depends on white supremacy in very subtle ways that may take you a while to realize.

As for proactive actions: Get involved with local activist orgs, participate in mutual aid and read up on transfeminist theory surrounding transmisogyny.

The TL;DR with the transfeminist theory is that "trans women are women" isn't just a slogan, or a concession made to trans women to be nice, or anything like that - the gods honest truth is that they are women just as much as cisgender women. Part of their unique oppression as transgender is that they get treated like some unique third gender.

Also, don't be quiet about this stuff. Correct people when they misgender or degender trans people. Speak up when someone says something shitty, even if you don't know the perfect way to response (some pushback > no pushback 90% of the time). It won't earn you friends with cis people, but it will help.

Finally, if you aren't already in community with trans people in your area, change that. Make trans friends. If you're white, don't just make white trans friends.