When I start a negotiation, I don't think about what's best for me, I think about what's fair. I think deeply about this and come at it from multiple different angles of where my personal jealousy-free line is were I on either side of the deal. And then... I just start there. I describe it in detail and elaborate on any nuance as needed.
And you know what, as a result people sure seem to like doing business with me. Negotiations aren't draining experiences, they get increasingly frictionless and the business relationships have tended to grow into rubber-stamp deals of my proposals. Also in my experience, increasing the velocity of transactions is far better for growth than trying to maximize selfish individual gain on any particular deal.
This also has worked for me in business, my personal life, and many other contexts. I've solved some really bitter, decades-long, emotionally charged disputes this way.