Will you buy your creation?
When you are in the process of creating something- a piece of art, food, a business- get obsessed with it. Make your mind think about it and dream about it. Surround yourself with material and information about the thing you want to create and take it all in.
Once you feel ready, share this information with people around you, of course they need to have the time for you as well as some understanding of the field.
Now let them sell your creation to you. Ask the difficult questions, the unbiased questions. Be ruthless.
If your creation cracks under this pressure, it is time to go back to the kiln. Make it stronger. Put it to the test again. And sell it only when you would be happy to buy it yourself.