Start by thinking about the problem you want to solve for people. Answer the question "what problem are we trying to solve and for whom", and let that answer guide everything from the tech stack, to the user expereince, to the business model and marketing. Once you've identified what you are trying to solve, and who you're solving it for, everything else should flow from that vision.
Do research from the beginning. Research will help you validate whether there is even a market for your product, what that market will pay for your product, what things are important to that market, how the market is currently solving their problem, and what solving the problem is worth to them and whether they are willing to pay actual money to solve it.
Aproach everything with a design thinking process. Design is not just how things look, and it's not something that happens after building something. Design is what you are building, why you are building it, and how you are building it. How things look is really just an executional detail. Every problem your product is going to solve should go through the design thinking process of identifying the problem, breaking it wide open, exploring solutions, and narrowing it down to the best one in implementation based on informed criteria.