I have come to the belief that the best policy a tutor can follow is to facilitate learning in the Writer during the session and to foster independent learning skills so that the writer may learn how to learn to succeed. I learned today at a Tutor Certification Workshop that Intrinsic motivation may be a large driver behind this concept.
Through discussion, our workshop group deduced that when you teach something to someone, they learn it that's good, but they don't necessarily learn how to learn without the tutor. When you ask them the right question though, well for example: If you're helping a student understand the concept of sensory details, instead of writing a short passage full of sensory details for them and then telling them why those details are called sensory details and what effect those have on the reader, it might be a good idea to have them think of what they've learned about sensory details, and then have THEM write an example, or at least vocalize one to you. Then, when they realize that they've got it, they have a feeling of success which is an intrinsic motivator. That success adds fuel to their confidence of grasping future concepts on their own.
To keep following this example, if they don't know about sensory details enough to write some, you could write an example, have them identify the details, and then ask them why those details are sensory. My limited experience has to lead me to the conclusion that if you can just involve the writer as much as you can, ask as many questions as you can, and get them to do as much of the work as they can, hands on work, facilitating the work that they do along the way, then you can foster their independent learning and reasoning skills as well as confidence in composition.