Here's a great article by Noah Kagan, outlining the steps from defining a business idea, to evaluating its market potential and finally testing its viability.
This should be a must-read for new entrepreneurs, as a step-by-step template for getting started without risking everything into a moon-shot startup. This approach may not make you the next Steve Jobs, but knowing how to do it will require you to learn many skills which are useful in any business.