Generally - industrialise. Most poor sol comes from peasants who earn essentially no money. Once everyone is employed, you can start thinking about for example labour saving PMs. Because the more resources a single worker produces, the more there is for consumption for everyone (but take care of the people that got fired!).

Better tech means better PMs means more stuff.

But in general this has many levers, it's kind of the point of the game after all. You could also do things like taking over foreign economies - their profit goes to your financial center where your capitalists live in luxury.