The one thing I have found that really helps here, for self-directed documentation, is to write it for a modified version of yourself.

You may still be the audience. But you will be four or five years older, shit will have gone on in your life, you will have more to remember, you will be tired, you will have less patience, you will resent being forced to do archaeology on yourself, and have a dim view of the irresponsible young scamp who thinks he has an excellent memory that you are right now.

Write for that person and your documentation will be better.

(As you may be able to tell, I am now that person. And I fear there are two more cycles of this to go)