Be a professional and treat all parties with respect.
Too often realtors treat the other party as an afterthought, or even worse, an adversary, which can create ill will and cause harm to their own client's best interests. Negotiations are not the time for ego, drama and spotty communication.
The most effective negotiators actively engage with the other party, practice stellar communication, and always treat the other party with respect. We're able to most effectively advocate for our clients when we adhere to these basic principles.