Ditto Nuclearo. I'm interested in from other readers who know more than I do, but I'll throw in my 2 cents: For added fun, use a long rope, do the waist wrap just like Nuclearo said, but instead of then going down (with the rope), wrap it around the waist one more time and pull the ends of the rope through the bend in the ropes next to the loop the ropes went through the first time. Now your bondagee has 4 wraps of rope around the waist (2 pairs of 2 strands each).
Carefully snug up each of the 2 pairs of waist ropes so that they're nice and tight, then pass the rope down between the legs, separating the 2 strands so that they are close to the inner thighs, not touching the private parts, then tie it off at the front (after pulling it nicely tight)!
Voila ! You just applied a unisex crotch rope, and if it's on a guy, you're finished. If it's a gal, you're about halfway finished.
For you're fine female bondage partner, don't tie off the crotch rope in front just yet. Pass it back down through the crotch, with one strand on each side of the (am I allowed to use that word in this forum

), between the (and what about this other word

). The part of the rope over those sensitive body parts can be nicely knotted, as Nuclearo suggested.
Pull the rope up and over the back of the waist ropes, then back down.
But instead of running the 2 strands back through the crotch for the third time just yet, stop and make a daisy chain with the part of the rope that will be touching the aforementioned unmentionables, and tie it off in the front after making sure all 3 runs of the crotch rope are tightened to your (plural !) satisfaction.
I'm going to give my thumbs a rest and get some real exercise before I mention 2 ways to tie a single crotchrope on 2 bondagees (unless someone beats me to that post).
Cheers!
I love tying and being tied up! Struggling hard but unable to escape. Mouth filling gag. Helpless. Vulnerable.