Be reasonable, don't expect to negotiate a win before the war starts, or no one will agree to war you, obviously don't give up too much in terms of timing or whatever advantages you might perceive, either. If you want a War without negotiating it beforehand, you are going to have to hit a KD that is bigger than you, give them some incentive to hit back and press the button.

If being nice and making friends who you can War cordially doesn't work, just start kicking people in the shin.