A new project usually arrives with more possibilities than it needs. A notebook becomes an app; a shelf becomes a whole workshop. The imagined version is exciting, but it can make the first step unnecessarily heavy.
Try a smaller question: what is the first version that would be useful to someone today? For a shelf, that might be one board at the right height. For a tool, one input and one clear result. For a notebook, a single page you would want to read again.
Give the first version a boundary
Write down what it does, what you need to learn, and how you will know it works. Keep that note beside the work. An idea that falls outside the boundary can wait on a separate page without joining the current project.
After using the first version, the next step tends to become more obvious. Real use is a better editor than an ever-growing plan.