One way, not sure if best way, is to have your CEO buy profitable state corps then use direct trading to transfer the money back to your CEO or main country. This won't give you direct money, but you do get free corps, and later you might IPO them.
Cancel all automation then close down remaining state corps and sell all of the country's products. Wait a month and you'll generally see around 500B, after that I usually like to exchange workers with the C3 and get some extra hte or whatever you need.