1) Not Negotiating

Via The Essentials of Job Negotiations: Proven Strategies for Getting What You Want:

…the overarching theme to successful job negotiations is to be respectful and reasonable at all times. Be sure to keep this guiding principle before you, and then jump in. There is some truth to the adage thatyou get half of what you ask for, and none of what you don’t.

7) Missing details by not listening carefully or by getting overwhelmed

Via The Essentials of Job Negotiations: Proven Strategies for Getting What You Want:

Make sure you place your full attention on everything the other side is saying, and are not thinking ahead to the next question you want to ask. Take a break from the negotiation any time you feel emotions getting the better of you, or feel your attention waning for any other reason.