Before you start writing, you should explore the different types of documentation and how they fit together. Topical guides, references and tutorials all belong in their own section.
Learn how to write documentation that is clear and effective. Keeping your documentation up to date and easy to read is important if you want developers to understand.
Pretty, usable documentation goes a long way! The content may be king, but the medium is the message. Don't turn away potential users before they even get started.
If your documentation is hard to edit, nobody will! Making documentation a large part of your workflow keeps it up to date and easy to manage.