It's funny that when people reach a certain age, such as after graduating college, they assume it's time to go out and get a job. But like many things the masses do, just because everyone does it doesn't mean it's a good idea.
Understand that relationships are more important than contracts. Business deals are relationships between people. The signed piece of paper is important, but it's merely the result of the relationship, not the cause. If the relationship crumbles, the contract won't save you, although it could be very lucrative for your lawyer.
It's important to note that you don't have to earn money from all of your interests. If you just dive in and pursue what you enjoy, you may be surprised to find out which interests help you generate income and which don't.
Pour the bulk of your time into action, not deciding. The state of indecision is a major time waster. Don't spend more than 60 seconds in that state if you can avoid it. Make a firm, immediate decision, and move from uncertainty to certainty to action. Let the world tell you when you're wrong, and you'll soon build enough experience to make accurate, intelligent decisions.
Saying no isn't easy, but it's a required skill if you wish to have any degree of focus in your life. If you say yes too often, you'll likely fall into the common trap of saying yes to the good while simultaneously saying no to the best.