Agile documentation should:
- Keep it simple (KIS), keep it lean (KIL).
 - Clear and unambiguous.
 - Lightweight, dot points, single sentences, to the point.
 - Consistent presentation with whitespace.
 - Well designed, organized, structured.
 - Prefer diagrams over words.
 - Easily searched and navigated.
 - Easily updateable.
 - Just in time (JIT).
 - Stable (dont document rapidly changing work).
 
Ideally documentation should convey information clearly, concisely, reduce information silos (i.e. knowledge only known by an individual/team) and reduce re-learning time across teams & organisations.
Reference Material
Extract from Agile Modelling:
Agile documentation principles
- The fundamental issue is communication, not documentation.
 - Agilists write documentation if that’s the best way to achieve the relevant goals, but there often proves to be better ways to achieve those goals than writing static documentation.
 - Document stable things, not speculative things.
 - Take an evolutionary approach to documentation development, seeking and then acting on feedback on a regular basis.
 - Prefer executable work products such as customer tests and developer tests over static work products such as plain old documentation (POD).
 - You should understand the total cost of ownership (TCO) for a document, and someone must explicitly choose to make that investment.
 - Documentation should be concise: overviews/roadmaps are generally preferred over detailed documentation.
 - Travel as light as you possibly can.
 - Documentation should be just barely good enough.
 - Comprehensive documentation does not ensure project success, in fact, it increases your chance of failure.
 - Models are not necessarily documents, and documents are not necessarily models.
 - Documentation is as much a part of the system as the source code.
 - The benefit of having documentation must be greater than the cost of creating and maintaining it.
 - Developers rarely trust the documentation, particularly detailed documentation because it’s usually out of sync with the code.
 - Ask whether you NEED the documentation, not whether you want it.
 - Create documentation only when you need it at the appropriate point in the life cycle.
 - Update documentation only when it hurts.
 
When is a document agile?
- Agile documents maximize stakeholder ROI.
 - Stakeholders know the TCO of the document.
 - Agile documents are “lean and sufficient”.
 - Agile documents fulfill a purpose.
 - Agile documents describe “good things to know”.
 - Agile documents have a specific customer and facilitate the work efforts of that customer.
 - Agile documents are sufficiently accurate, consistent, and detailed.