Writing as a Form of Thinking
You do not write to record a thought. You write to find out whether you have one.
The draft is the thinking
There is a common fiction that writing begins after thinking ends. In practice, the two happen together.
Sentences are tests
A sentence either holds or it does not. Writing gives you a way to run the test.
Revise with your ears
Read it aloud. The places where you stumble are the places where the idea is still incomplete.