There were two basic principles that underlay Dr. King's actions in the Civil Rights Movement.
The first of these was his goal--the goal of racial integration and brotherhood. This principle set him apart from black nationalists like Malcolm X who wanted blacks to remain more separate from whites. This principle helped make King seem more acceptable to whites and was much more in keeping with what the general idea of what America should be.
The second major principle was his commitment to nonviolence. The nonviolent nature of the Civil Rights Movement was a major reason why it succeded. People across America came to sympathize with the movement as they saw peaceful protestors being abused by police. The public would not have been nearly as sympathetic if the protestors had used violence.
These two basic principles were the major causes of the success of the movement that King helped create and lead.