Find a local lefty group (anything from Food Not Bombs to SRA). Participate, listen, organize, help people where you can. I live in a remote rural area and I still have half a dozen small but active groups to choose from, you just have to get out there and find them.
Can you describe where you found your local groups? And particularly helpful web searches you can share? Searching for <location> lefty groups does actually give results but I welcome any suggestions
The two biggest things you can do are to get organized and read theory. All the Leftists in the world thinking really hard won't make a difference if they don't organize. If you're interested in Marxism, I have a "Read Theory, Darn it!" introductory reading list you can check out if you want, complete with audiobook versions of every work listed minus 1.
Honest question, how important is reading theory? Won't we need to build our numbers beyond where it's reasonable to expect everyone to have read theory? Especially given that much of it is written in an academic rather than a narrative way. Obviously there should be those in the movement who are versed in theory, but shouldn't the movement be open to as many as possible? And assigning homework as soon as they want to join seems like a good way to discourage engagement.