I tie mine so that there is just enough room for your release to fit. This way, the loop will stretch a tad after you shoot a few and give a better fit. I tinker with the knot end till they are tight agaist the rest of the knot and you have just enough room for the release. After you do it a couple of times, you get better at guessing it right the first time. One thing though, make sure when you burn the ends to make them mushroom out as much as you can for added insurance.

Nock point. I usually start at 1/8 above center. Keep in mind that its just a starting point. Once you shoot through paper you will be able to tell where to go next with it. 3/16 is fine though, just shoot through paper and see what the tear tells you to do.