From my experience there are no hard, fast rules to the art of negotiation. And generally speaking the more natural, transparent, and reasonable you are during a negotiation, the more effective you will be.
I don't agree 100% with all these, but I think this article includes several useful tips for entrepreneurs or anyone during a negotiation no matter how big or small.
1) Don't use the word "between."
2) Avoid saying "I think we're close."
3) "Why don't you throw out a number?"
4) You never want to say "I'm the final decision maker."
5) No need to ever say "F#$@ you."
Read the full article here which is packed with useful examples.