IMO the most important thing is to read theory, read the history of leftist movements, and use good research practices. Just keep reading critically, try to follow the authors’ arguments, and internalize the things you understand and like. Also, it’s more important to build up a coherent worldview than it is to fall into a specific ideological box.
For anarchist literature, The Anarchist Library is an incredibly diverse resource of often contradicting viewpoints, whereas the Anarchist FAQ is (in my view) an excellent first place to look for detailed explanations for commonly asked questions. In my view, the Anarchist Library is an excellent example of how it is important to develop your own worldview. Because the most anarchist/communist/socialist/leftist thing anyone could possibly do is loudly and vehemently disagree about something with someone who otherwise agrees with you 99.99%.
IMO, this is legitimately how progress is made, by exploring the space of ideas. And that means that every once in a while, there’s going to be some ridiculous take from someone who is otherwise on your team who’s trying to explore that space of anarchist possibilities. So even when drawing from resources you typically agree with, it is so important to think and read critically.
For Marxist and state-socialist literature I’m honestly a lot less informed since…well…I’m an anarchist and I’m going to disagree with statist Marxists on a lot of issues. But when I do need to look up some non-anarchist literature, Marxists.org usually has what I need.
This is true and I’m definitely guilty of reading too much into stuff and not doing enough stuff… hence why I’m laying in bed procrastinating on the stuff I’m supposed to be doing… but I do think that some theory is really important to have. Like, what are we aiming for, why did some projects fail and others succeed, what are the common pitfalls and how can we spot them, and how can we better refine our arguments for the rare times we do get a platform?