Socialism

Look for leftist organizations near you, join them and honestly engage with them.

Personally, I found Palestine protests and similar ones to be a great way to find multiple parties, ask them basic questions, and separate the junk ones (e.g. idealistic ultra-left sects) from the ones with a viable strategy. I first went to the unionists there and asked them if any of the socialist orgs actually worked with them and only two of the four locals were mentioned. Notably, one which was mentioned and one which wasn't were both, on paper, followers of the exact same strain of Trotskyism, in fact one was a split from the other party, but on the ground it's night and day, apples and oranges; one works with&within unions to make sure its members are on board with picket actions before they happen, the other has fresh college students recite an evangelical recruitment script at protests and end up asking Palestinians at a Palestine protest with family still in Palestine if they're aware of the ongoing conflict.

In a word, if you have choice, check them all, and you don't have to pick one just for their theoretical tendency. Being correct isn't enough.