Even by simply walking through the stacks, a librarian will become familiar with the library in a more practical way. Make sure patrons get what they came for. At Home Depot, the employees always make sure that their customers leave with the things they need. They ask questions, are able to suggest better items, and are able to direct customers to appropriate areas of the store. Sometimes the chief executive himself puts on an apron and walks the floors, helping his employees provide top-notch service.
Librarians can do the same thing.
This question-asking can't be stressed enough as a primary form of customer service. A model for this type of service can be seen in the restaurant business. Go to a good restaurant and listen to the server. He constantly asks questions before the meal, during the meal, and when you're paying the bill. Before the meal, the server will take your order and ask if you'd like anything else.