I think good documentation is very hard like most developers. Code writing easier then documentation for it. But, I saw below lines when I was reading documenting your project section of Expert Python Programming book and I liked them. These rules are currently hanging over my desk. Perhaps you would like it share exactly.
- Write in two steps: Focus on ideas, and then on reviewing and shaping your text.
- Target the readership: Who is going to read it?
- Use a simple style: Keep it straight and simple. Use good grammar.
- Limit the scope of the information: Introduce one concept at a time.
- Use realistic code examples: Foos and bars should be dropped.
- Use a light but sufficient approach: You are not writing a book!
- Use templates: Help the readers to get habits.
If you didn't read this book, you really should read it. This book is not about just Python. Refers to many subjects related to programming. Even if you don't Python programmer, you can learn so many things.