A tie on nock is just a series of over/under knots. Start by placing the serving materiel under the bow string at your nocking point, pull the ends of the string to the top of the sting, and tie a overhand knot. Next, pull the ends of the serving material down to tie a overhand knot on the bottom of bowstring. Alternate top, and bottom knots 8/9 times, then tie off by reversing your overhand knot, cutting the nock string, and burning the ends off.
You adjust you nock point by screwing it up/down with your thumb and index finger. Might be tight, but it works just fine, and wont' move unless you screw it up/down yourself.
Best thing to do, buy a "Vapor Trail" string set up (won't stretch), use a bow square to place the nock where you want it, tie it and forgett it.
Here is a link showing you how to tie on a nock http://www.bowsite.com/bowsite/features/practical_bowhunter/tieone/
Hope this helps.