The core teachings of Zen lie beyond words and concepts. Historically the teachings are passed on from teacher to student, a mind to mind transmission. In Zen, the teacher/student relationship is central. It plays an important role in assisting a student grasp and live out the teachings of our ancestors.
Zen teacher Norman Fischer speaks about this in an article from Shambhala Sun magazine: “In most traditional meditation-based Buddhist practice there is a tremendous emphasis on the centrality of the teacher and the idea that insight cannot be learned from books nor is it a matter of mystical intuition. In order to be liberated from self-attachment, the student needs to let go of self-view, and this is nearly impossible to do alone, since self-deception is so natural.”
So this is to say that a good guide is very important to move forward in our practice, someone who knows the spiritual landscape and whose insight has been sanctioned and approved by a realized teacher themselves. The teacher student relationship then, is a wonderful way to check and expand our insights and realizations because in our solitude we can deceive ourselves.

There is no one formula for the teacher student relationship but the most important part is knowing that the job of the teacher above all else is to show the student what Zen practice is by assisting him/her to find it out for themselves in their own way.

Once the student realizes the need for a teacher to guide and deepen their practice it is important to find one who is compatible and who the student respects, and wants to “dance” with even if he/she gives students a hard time. A teacher is not going to be like a kindly parent or grandfather all the time and the relationship is not like psychotherapy although psychological issues may come up.
A teacher should be a guide pointing the way by being a living example of how to break out of the ego shell and awaken and may teach this in a variety of ways including actions, or words sometimes soft sometimes harsh. 
In this process a teacher may suggest or say things that you don’t like or rub you the wrong way. A Zen teacher is not always going to be pleasant and easy. A part of the teaching is to help the student meet their “edges” which means to look at where the student is holding on to some ego idea, concept or belief and assist them in recognizing their holding and in giving them up. I remember a story of one teacher whose students were not paying attention and taking the teachings for granted. One day in daisan he placed a pumpkin on his cushion. Zen is full of stories about teachers who use “skillful means” and sometimes unique and creative methods to awaken students.

To build this kind of relationship lies in developing trust. The student has to practice trust and the teacher trustworthiness. This is an ongoing and fluid relationship. The teacher takes care of the student guiding his/her development. And the student supports the teacher in their work by helping in service positions in the zendo, attending sesshins or perhaps financial support. 
The final goal though for any teacher/student relationship is for the student to surpass the teacher not by being better but by becoming themselves. My own teacher Roshi Kennedy told me, “I want to encourage you always to be yourself, not to be a clone of me or anyone else. You must see the dharma in your own way. The goal of Zen is to become yourself. When you become you, Zen becomes Zen.” His words were so important to me. He only wanted to sponsor me to be who I am. In that moment I felt loved, validated and safe within appropriate boundaries so I could do my spiritual work. He did challenge me to expand my insights but the relationship was not about my being controlled, dominated or unduly influenced. It was his commitment to giving guidance and encouragement to me as I walked my own path.

The final goal of this kind of spiritual relationship then is when the student matures. At that point the teacher may at times learn from the student as well. The student and the teacher then mutually support one another. Dogen Zenji wrote that he was open to learn from an infant and would teach an old man if it would help. He meant that any teacher worth his/her salt is always a student, always ready to deepen their insight including learning from his students. In this way the teaching circle is complete.