Get out of the building and talk to potential customers.
You might have a vision of your product, but this vision is just a bunch of hypotheses. If you try to build a product without validating them first, you may waste a lot of time and resources. You can do it in a better way - talk to potential customers before you build anything, and get a better understanding of who they are and what problems they have.
Make a list of all hypothesis that you have.
Do not assume anything. Instead, put it on the list with the hypothesis. There are two major hypothesis everyone has: the value and the growth hypothesis.
Brainstorm what you need to do to validate them.
Some of them you can validate by talking to potential customers, but with some of them, you will have to wait until you have the first version of your product.
Get out of your building and talk to potential customers.
Try to understand them and their problems.