How? Small steps, most of them logical and obvious, such as:
change performance appraisal guidelines so that knowledge sharing is taken into consideration
find out about someone’s knowledge sharing habits not by checking the amount of posts on the intranet but by asking their peers (check for quality of contributions and willingness to help, for example)
use knowledge audit questionnaires and interviews to gather data (obviously!) and to, simultaneously, emphasise the behaviours expected from staff
have idea banks but make the idea cycle completely open and transparent so that ideas are owned and worked on by all those interested
review the way the organisation rewards and recognises new ideas, new business, good results, etc..
