nock high or low on your arrow flight is most often a function of the location of your nock point on your string. If you are nock high on your arrows you move your nocking point on the string down to adjust and vice-versa.
Other things can cause this too however. You might be torquing the bowstring when you draw it back causing the arrow to flex before you even release it! Be sure to RELAX your entire right hand all the way back to the elbow--but especially the wrist-- before you draw. Just go limp and only use enough tension in you fingers required to hold the bowstring. For people who torgue the bowstring like me, I also feel it helps if you get as much of a hook as you can get on the bowstring with your fingers. For some reason this reduces the tendency to torque the string.
Lastly, only make one adjustment at a time and shoot the bow. You won't know what's causing it by making two adjustments and find it goes away... If you move the nock point....then try it. Change your drawing form...go shoot it. But not both at the same time.