Standard procedures while eliciting requirements need not stop with interviews, reviewing documents and validating diagrams. It needs corroboration and information gathering on the fringe too. Some interesting practices in this regard.
Reading notice boards is a good practice. This is especially true in factory premises. It gives a good idea of events currently happening and an insight into current relationships in the organization
Reading the house magazines gives information current topics being discussed in the organization. It also gives information on opinions and interests of the contributors in the magazines
Internal Telephone Book
This is invaluable. Telephone books would cover all departments, divisions and locations in the organization. This is a good document to track coverage of the interview checklist. Visitors Register If possible, this is a good source to understand who the external agencies the organization is interacting with are.
Some additional skills
My favourite one is the ability to read upside down! Amazing how this helps.