Before the shot, before the nock ever leaves the string, you need to be assured that the string loop on your bow is tied properly. Do not be that guy at the bar who tells the story of how he missed a giant, because as he drew back on an old string loop, and ended up punching himself in the face when the loop broke.
A string loop that is too loose will cause inconsistent arrow flight as the nocking point will be different with each draw cycle. The end result will be arrows that land above and below the target. A string loop that is to narrow will pinch the nock and cause it hit off its mark as well.
There are about 100 different videos on Youtube that can help you learn how to tie the loop itself.
Here are some simple tips to help you tie a string loop successfully.
Use a high quality string loop material that will create a nice mushroom top on the string when you melt the end with a lighter. Failure to do so will result in knot slippage and thus loop failure. BCY makes excellent string loop material.
Leave an arrow attached to the bow string to ensure the correct placement of the string loop. This will give you the exact placement of where the string loop needs to be. Constantly check to ensure the exact placement of the arrow in relation to the arrow rest.
Use a pliers to tighten your first knot. Don’t pull on the part of the string that will be in the loop. Once the loop is tighten, if it needs to be adjusted up or down the bow the string, rotate the knot clock wise to move it up the string. If you need to move the knot down the string rotate it counter clockwise. If you try to push the knot up or down the bow string, you will move the serving string and not the knot.
With the arrow in place begin to tie the bottom knot. Pull the string tight until it rests against the top of the knock.
After you tie the second knot, make sure that it is resting securely next to the nock. Use your pliers and pull tight.
After you cut off the excess string loop material rest your razor blade on the top of the knot.
Use a piece of neoprene for an old can koozie to protect your had from the heat of the lighter. As you melt the end to create your second mushroom for the knot, build it slowly and carefully, so you do not burn the bow string or the string loop, the razor blade will help to protect the loop from the flame.
If your knots are slightly uneven, do not panic, the next step will fix that.
Use a string loop stretcher to tighten the knot, and set the length of the loop.
When you are finished the string loop should rest next to your nock with approximately 1/16 of an inch max on either side.