How do your sims MOSTLY earn the living?

There should also be an option for "all of the above." Most of the time my sims will have their career, and then a hobby that makes them money, like gardening, writing, a musical instrument, painting, etc. That's the best way I've found to make money in game if you don't want to cheat. Gear everything towards work in the young adult stage, or maybe even as a teen, and then by the time they are adults they should have a pretty nice nest egg, specially if you get the Wealthy Aspiration reward that gives you weekly investments on your funds. Sometimes, however, I have my insanely rich sims gift large sums of money to their friends or ex-lovers. It all depends upon which sim I'm playing.