Building a knowledge sharing culture requires that you involve business users in development of your knowledge management solution early and often. Here are some suggestions based on my experience:
You can begin to get your business users involved in the building the knowledge management solution by having them help to identify the documents or other content that has the most value to the business. I recommend that you have business users participate in creating and applying the metadata or taxonomy that will apply to the documents. The more precise you get in describing content, the easier it will be to find later. By getting the community of users involved early you can begin to explain knowledge management to them. The early participants and adopters can act as evangelists later. With user feedback you can identify and tag the most valuable material so that when users perform a search it appears at the top of the results list.
There are other ways to begin to build the culture of sharing. You will need to explain to your business users: "What is in it for me". They need to understand in a profoundly personal way how they will benefit from the KM initiative and how their work will change. This is usually done with anecdotes about a success that resulted from sharing knowledge. You can find examples of when your company performed the best; when everything worked just right, and ask people how it felt when that happens. Most of the time, the best practice involves collaboration, working as a team, and sharing knowledge to win new business or deliver a high quality product. The KM solution will enable the company to function like this more often. The objective is to find a story you can tell about knowledge sharing that is very positive and attractive. People can then begin to imagine how knowledge sharing will help them with their work.
In addition to working with the business users, it's critical to have visible top management support. This will not require much of top management's time, but they will need to demonstrate their enthusiasm for knowledge management frequently. They need to be convinced that this is an initiative that will create meaningful results in the business and they need to lead in that direction.
I recommend communicating frequently to business users, explaining the KM planning and rollout and how it will benefit their work. Don't overpromise, but keep them well informed. Show them example screen shots of the search page, or other functionality that will make their lives easier. You can use "use cases" or scenarios to demonstrate how people will use the new tools. This process of building actual scenarios that explain how users will search and apply content is very powerful.