Argument Vs. Opinion: How do You Negotiate?

The thing to know before negotiating is: its not about winning; its about compromise. This is no secret. The thing about a successful negotiation is that everybody comes out of it feeling like a winner. That is the secret. If even one party feels like a loser, it is not a successful negotiation- because if you feel like a loser, you don't buy into the followup action and you don't trust the other party - ever! That's how we are.
How do you negotiate?
Do you distinguish between an argument and an opinion? Keep personality, judgement and value systems out of it? Approximating Samuel Johnson - opinion is like an arrow shot from a bow; as strong as the man who draws it. "Argument is like an arrow from a cross-bow, which has equal force though shot by a child.... You cannot help paying regard to their arguments, if they are good." Conduct negotiation with arguments, not opinions. Arguments stand on their own (like proofs in geometry) and open doors for learning for all parties and in taking the discussion forward. Opinions are shutouts implying judgement, a value, around which there can be no acceptable compromise, thus forcing the other party to get further entrenched into their starting position. To help yourself do this in real time, enter a negotiation with the idea that you will learn at least one new thing. Identify assumptions and preconceived notions (consultants call it frames of reference) if you can before getting into a negotiation.
Fortunately, on the way to acquiring a win-win mindset, there is immediate help in the form of value neutral language. Yes, watch your words. Is a value judgement inherent in the word? Get rid of it. One person's irritant is another's joy. A rose bush in a wheat-field is a weed but a wheat-stalk in a rose garden is also a weed. Pollution implies bad stuff but emission is value neutral (emission can be good or bad, e.g. breathing is a good emission).
And lastly, when a negotiation fails, it is generally a failure of process - since nobody goes into a negotiation unless desirous of a solution (the other type is called posturing :-) or just to lose. So when things do fail, let it go; don't let it stop you from going back to the table.
Relationships allow you to work things out, even becoming stronger in the process. A negotiation is the first investment in building a relationship.