A usable client document set has six parts: the company overview, the network diagram with addresses, the systems and application register, the account and access matrix, the standard procedures (onboarding, offboarding, backup, restore, common faults), and the vendor and contract list. That is it — six documents, kept current, beat a hundred stale pages.
Write procedures as numbered steps with expected results, not prose. 'Step 4: assign the Studio-Staff group. Expected: licence appears within 15 minutes.' A step without an expected result cannot be verified by someone new.
Never store passwords in documents. Reference the password manager entry by name. The document says where the credential lives and who may use it; the vault holds the secret and the audit trail.
Update documentation as part of the ticket, not as a project. Every closed ticket asks one question: did anything I learned change the documents? Thirty seconds per ticket keeps the set alive; a quarterly documentation project never happens.