The best method for negotiation is to know your minimal self.
There are many tactics and theories taught by many people. There is the “I don’t need you, I want you” tactic—also a truth. Then, the “you owe me” and “that’s your problem” tactics, plus the famous “over-aim to get what little you want” tactic.
But, the best method is to know your minimal from the beginning, declare it from the outset, and stick to it.
If you can compromise a point after 20 hours of talk, you never really wanted it in the first place. You should know that.