Keep lots of ideas banging around in your head

Having multiple hobbies allows your brain to subconsciously compare and contrast problems and solutions, forming new connections at the margins of each.

Via Where Good Ideas Come From: The Natural History of Innovation:

Legendary innovators like Franklin, Snow, and Darwin all possess some common intellectual qualities— a certain quickness of mind, unbounded curiosity— but they also share one other defining attribute. They have a lot of hobbies… That cognitive overlap is what makes this mode so innovative. The current project can exapt ideas from the projects at the margins, make new connections.

Work on projects because of passion, not money

This is what produces the best art and, eventually, the most success.