A very good place to start

I have come to a frightening conclusion:
    I am the decisive element in the classroom.
    It is my personal approach that creates the climate.
    It is my daily mood that makes the weather.
    As a teacher, I possess tremendous power to make a child's life miserable or joyous.
    I can be a tool of torture or an instrument of inspiration.
    I can humiliate or humor, hurt or heal.
    In all situations, it is my response that decides whether a crisis
    will be escalated or de-escalated, and child humanized or de-humanized.

Haim Ginott (Teacher and Child, 1972)

from http://inthemiddlewithmrd1.blogspot.com.es/