Complete your jewelry project and make sure that the beads or other notions on your jelly string are complete and in the correct order. Also make sure that you have left ample room to tie a knot on the jelly string. Try to leave at least eight inches of jelly string for a square knot. You can cut away leftover string once the tying process is complete.
Tie one single overhanded knot, just as you would when you are tying your shoelaces. When you have finished, the string should form an "X" when held open with your hands. Take careful note of which string is in your right hand and which string is on your left hand.
Pass the string in your left hand over the string in your right hand. At the same time, pass the end of the string in your left hand under the string in your right hand, through the opening that the two strings have created. In this way, you will have tied another knot in the opposite direction from the first knot.
Pull both ends of the jelly string tightly at the same time. If possible, try to secure the first knot by holding it down on a flat surface with one finger while tightening the knot. This will help prevent the knot from slipping open while you are tightening the elastic string.
Maintain pressure on the knot, to help maintain tightness and to compensate for the natural elasticity of the jelly string. Apply equal pressure on all strings as you pull them to tighten the square knot. If done correctly, each side of the knot will only have one of the strings coming out of the knot on each side, as opposed to both strings coming out of each side of the knot.
Apply a small dot of rubber cement at the center of the square knot that you have tied. This will reinforce the knot and prevent it from slipping and loosening. Rubber cement is also flexible enough that it will not crack or break with use.
Allow at least two hours for the rubber cement to dry thoroughly, or as stated in the manufacturer's directions. Once the knot is completely dry, you can trim any excess jelly string from your project and begin wearing your jewelry immediately.