I don't really agree with this. I've had to mentor people and there is not really a special trick. I just kind of pair program, and when we start I drive and eventually they drive and then once that's comfortable I leave them alone and leave them to ask me questions. I've found this mostly effective.
Explaining things to junior developers isn't so different from explaining things to anyone else. In the course of your job you probably have to explain concepts to your co-workers and to non-technical people, right? A junior is somewhere between those and you can calibrate as you go.