hmm broad question. every choke is a slightly different squeeze. for rear naked chokes, I would say with the hand behind his head, push forward and down, then with your other arm, try to have your shoulder and wrist touch each other and then flex your bicep last. For a darce or arm triangle, I always use the rear naked choke grip. You squeeze inward and then try to touch your elbows together. For guillotines, I also try to drive my shoulder into my wrist. also, remember to always be as tight as possible before squeezing on any choke, keep your elbows attached to your body, and be aware of where the pressure is and aim for the carotid artery. If it doesn't work, you probably aren't doing it correctly. Understand how to do moves correctly before drilling, so you don't drill a move that doesn't work.