I still like the painting club. I'm using one right now in the save I'm playing today because it fits well enough with my sims character type. It's cheaty and of course you need Get Together.
You can also basically go about your business as other sims are making money for you and getting better at painting when they do. I just buy as many easels as I can afford and add to them so there are almost twice as many as club members eventually. That way they can go from one to another. If you don't feel like interacting you can drag finished and abandoned pictures to the wall and sell them or dispose of them when you get a chance too.