Capture the first thought
The hardest part of writing is often beginning. Open a new note and put down the first sentence before you worry about structure or polish. A rough idea can become a list, a paragraph, or a full draft later. Give the note a title you will recognize, even if it is only a working title. When your thoughts change direction, create another note instead of forcing unrelated ideas into the same page. Keeping the first step easy makes it more likely that you will return and continue.