Drastically increase demands with each offer. Let's say you are selling your car for 10k. If someone makes you an offer for 8k, let them know the car is now for sale for 12k. If they come back with 10k, the car is now 14k. Keep a straight face the whole time and even appear agitated if they push back on your increased price.
Repeat demands. Every chance you get, repeat your demands, especially if they've been shot down. Do not take into consideration things like feasibility or if something actually exists in the modern world. For example, demand someone from another country attend the next meeting, even if it's physically impossible for them to get there in time.
Always immediately pull the nuclear option. Do not show any weakness. If they threaten to not meet your demands do whatever you can to make their life miserable. The more public the better. For example, if you're negotiating your salary and the hiring managers pushes back, go to a social gathering you know the hiring manger will be at and scream, kick and hurl insults at them in front of their friends and family until they concede.
Wear them down. This is probably the most important one. Keep an eagle eye out for the times they are tired, hungry, stressed, or extremely busy and this is when you pounce. Bother them so frequently that they'll give you what you want just to have some peace in their life. Let's say you try to to sign a deal with a customer. Call their cell phone every 10 minutes, 24 hours a day until they sign.
Best of luck in your negotiations and a special thanks to the negotiation master, my son Aiden (2 years old) for teaching me so much about the art of negotiation.
