Try to understand what skills and experience will be most valuable to your successor. The strengths that enabled you to build up the business may not be what he needs to take it forward in the future.
A common approach is to have your successor work in different areas of the business to familiarise himself with it all. It is also often a good idea for your successor to get exposure to new ideas and different ways of doing things. This can be accomplished by working for another business, and through suitable training.
It's usually helpful to work towards a planned handover date. During the final month or two, your successor can work alongside you. You can also use this time to ensure that he has all the information he needs, and has been introduced to all the key contacts within and outside the business.