Write out your plan, and stick to it.
When you develop your plan, you should ensure that there is a clear timetable, so those involved know exactly what will be expected of them and when. Vague time references should be avoided.
For example, if your plan is to continue working until the day-to-day responsibilities become too much to handle, this could mean that your successor is waiting for the inevitable - illness or death.
One final point to keep in mind is that once you have set a specific timetable, you should stick to it. If the timetable is not followed, the credibility of the entire plan will suffer greatly in the eyes of all involved.