Organize and educate yourself. Develop an understanding of Marxist Historical Materialism, especially by reading Lenin and Mao.
The first thing to understand is that there is nothing valuable you can do as an individual to advance Communism. Communism is not an Individualist ideology. The first step is to find or build a local group of like-minded individuals. Once you've done that, you can ask, "What should we do?". There is no substitute for meeting real people in real rooms in real life.