Try living together. Living with your idea for a while will help it gel in your mind. Some creative types experience an entire concept instantly – they can visualize the sculpture or they can see exactly what the new store or restaurant or product will look like. For others, a bright idea appears, followed by a series of related concepts which fit like a puzzle around the main thing. Before marriage, before committing anything more than your own imagination, give your idea some time to evolve.
Try seeking out comparable ideas. There is no new idea under the sun. Whatever you think of next, it is not entirely unique. Even Apple computers carry parts from earlier models. Find out who is doing what you want to do, and try connecting with people involved. Why are they successful? Why are they failing? Gather some facts so you can learn from other people's experience.
Try finding experts willing to help you. Expert accountants can help you determine what your idea might cost in dollars. Expert legal folks can help you understand the regulatory or licensing hurdles you need to overcome. Graphic Designer Kathy told me her customers are mostly start-up businesses. She routinely talks them down from too-big launches. "You don't need to do everything at once," she explains. A simple website, a logo that can be used across the brand... starting a business on a shoestring is possible. Trust experts when they tell you to scale back your ideas. If they advise to go big or go home, go ask a few more experts before you invest any more time or money.
Once you know whether you want to pursue this idea, once you're organized and you have a few good people to lean on, you are well on your way to flipping the switch that changes a good idea, a lightbulb moment, into a shining, successful reality.