Hands-on use of product is the most efficient and effective approach to technical documentation. Use it. Write it. Test it. That's my motto, and it mirrors my documentation process.
After releasing content I strive to get feedback from users. I provide a user-centric approach to both technical and non-technical documentation:
Customer feedback
Support ticket analysis and escalations
Doc testing
PoC (Proof of Concept) meetings
Google Analytics
Support call monitoring
IT staff shadowing
User forums