Ship the walking skeleton

A walking skeleton is the smallest version of your system that works end to end — ugly, minimal, but alive.

Build it first. The moment data flows from one end to the other, every risk in your project becomes visible and testable. Integration problems surface in week one instead of month six.

Then fatten the skeleton feature by feature, keeping it walking the entire time. You'll never have a big-bang integration day again, because every day is integration day.