Learning media criticism, history, political economy, and how past groups have organized takes a decent amount of time. Namely, socialist theory. So does unlearning the ideological falsehoods that cloud our ability to think and investigate. And so does recognizing what builds power, what actions are effective, what cooption looks like and how to counter it, etc. So I don't recommend just doing one thing, but instead working from where you are to be closer to a stronger consciousness. I suppose the closest thing to a single recommendation I can give is humility and curiosity around all of the aforementioned topics and to give people grace IRL when you begin working with an organization.

If you are interested in reading recommendations and info about your thoughts on politics I'd be happy to think of something you might appreciate. Or if you feel like you're ready for action and are in the US I can recommend some orgs that are reasonably good to "start" with (many stay in them and that is also fine!).