The way I've seen it, you just tie it like a tourniquet right under your knee cap.
Personally, i've had cartilage removed from my knees and my ligaments don't restrict movement as much as they should for lateral movement. I end up using a light knee brace (so that I don't pull out all my leg hairs) and then duct tape my knees together using four strips. I create a diamond shape around my knee cap. I then do a complete circling around my thigh and calf in order to make sure the previous duct tape doesn't come off.
Others might have their opinions, but this works for me.