https://developers.google.com/tech-writing/two/summary

Summary

Self-editing

• Adopt a style guide.
• Think like your audience.
• Read documents out loud (to yourself).
• Return to documents well after you've written the draft.
• Find a good peer editor.

Organize large documents

• Outline a document. Alternatively, write free form and then organize.
• Introduce a document's scope and any prerequisites.
• Prefer task-based headings.
• Disclose information progressively (in some situations).
• Consider writing the caption before creating the illustratio

Illustration

• Constrain the amount of information in a single drawing.
• Focus the reader's attention on the relevant part of a picture or diagram by describing the takeaway in the caption or by adding a visual cue to the picture.

Sample codes

• Create concise sample code that is easy to understand.
• Keep code comments short, but prefer clarity over brevity.
• Avoid writing comments about obvious code.
• Focus your commenting energy on anything non-intuitive in the code.
• Provide not only examples but also anti-examples.

Others

• Make a practice of continuous revision.
• Provide different documentation types for different categories of users.
• Compare and contrast with something that readers are already familiar with.
• In tutorials, reinforce concepts with examples.
• In tutorials, point out dragons.

Further reading: https://developers.google.com/tech-writing/resources