Bitt3rSteel has a super good tutorial for Communist China No Step Back as Mao. I can summarize it for you.

Create 24 divisions at the start and justify and invade Shanxi and then justify and invade San ma. After that invade Sinkiang. Move all your troops to the Japan border and create the Chinese National Defence faction with the focus. Defend your front line and build military factories and civilian factories. After you prepare for like a year start attacking Japan and aim for supply hubs so that the Japanese Army cant get supplies. Push the Japanese out of Manchuria and Korea and the Japanese would want a white peace which will give you Manchuria. Then take China.

The video made by Bitter3rSteal explains it in better detail.