Start with the core

If you begin your new product, start from the core functionality. Not the core of the system or architecture.
Ask yourself: What’s the most important feature you cannot live without? Just name one, only one. Build this first and only. Eventually refine or redo if it doesn’t suit your needs. Then continue with the next. You always have a minimal but useable product and can stop anytime.
We once had to develop a web based system where users can file an application which can be reviewed, changed, rated and finally accepted or declined. We started with a web page where you could download a PDF and an email address to send it to when complete. Minimal? Yes. Useless? No. All the functionality which was needed was there. All other stuff could be done via email or phone. It was readily available and useable.
Start with the core.