Forget writing what you know. Write what you noticed that everybody else walked right past.

Knowledge is widely held, and a piece built only on what you know competes with everyone else who knows it. What you noticed is different, because noticing is not distributed evenly and much of what registered for you did not register for the person standing next to you. That part cannot be looked up.

Go back through a familiar subject and hunt for the detail you have never heard anyone mention. Build around that instead of around the summary you could have written from memory.