Usually if I am using a new string, I tie on the nock a little loose and short until the string breaks in (I can move it easier). When I have found the correct nock point and the string if broken in, I will take them off an retie a much tighter and longer nock point that will not move. I also use a serving thread for the nock, but make sure it is smaller then the string serving.

But, I also check the nock point and brace height quite often.