Leaving your job and training your replacement? There are four simple rules to effective knowledge transfer: create independence, work together, plan and give yourself the time to do these things.
First and foremost: assume that you will not be available to answer any more questions after you leave. Even if you’re staying in the same company, just in a different role, you need to teach as if you’re joining the mission to Mars. If you create a dependence on yourself by constantly saying “oh, just e-mail me when you need this” you’re going to make life very hard (and unimpressive, from the bosses’ point of view) for yourself and for the person you’re teaching. In a related note, nothing is too trivial for a knowledge transfer. If you know it, your replacement needs to know it.
Don’t do a Show and Tell. Work together: write documents, write code, write tests. You teach much more when working than when explaining some theory in front of a slide show, and seeing how your replacement works will tell you where to put some extra effort.
Plan your work. If you don’t have a plan you’ll jump around, which is both confusing and liable to make you forget whole topics. You also can’t asses times without a plan of what you’re going to cover.
Which brings us to time. You have to be realistic about how long you need to spend on a knowledge transfer; one day is not enough. And don’t forget – there is only so much information a human can pick up in a single day, so if you’re planning a series of twelve hour days – you’re planning to waste half of your time.