Customers will tell YOU what they want; So Listen! You can have what you believe to be a great product, but if your customers don't agree then your screwed. Makes sense right!
They will also tell you when good, is good enough. Don't spend crazy hours polishing the chrome on a new product. It is far more important to listen to your customer, then get them a workable prototype that meets their primary pain points. Help them.
Once they are no longer in pain, talk to them some more and then continue to listen and make changes to your product. Seems simple, but far too many business owners sit their shooting for perfection, and while doing so someone else beat them in the market.
The world is moving fast, so you better help your customer solve their problem faster than anyone else. If you don't you get left behind. We are not a patient culture in case you missed that fact!