A good negotiation should be fair and reasonable to both sides.  It is very important that the accused is aware of the maximum sentence permitted by law before determining whether the plea offer is fair and reasonable under the circumstances.

Attorneys who fight during negotiations are probably bad negotiators.  Even children know that, when negotiating, "you catch more flies with honey than you do with vinegar".  If a young child wants the child's mother to buy the child a candy bar, the child might tell the mother that she is kind, beautiful, and wonderful.  If the mother says "no", then the child might bargain by saying "I will clean my room if you let me have the candy bar".  If the mother says "no", then the child might remind the mother how good the child has been all day.   If the mother still says "no", the negotiations might end and the child might have a temper-tantrum (fighting).  The child having a temper-tantrum will probably not get the candy bar and might even get punished.  Fighting is for trial; not for negotiating.  To be a good negotiator, the criminal defense attorney should be logical, reasonable, and rational.

It is unethical for an attorney to guarantee that the attorney will be able to get the client a certain deal.  That attorney is "selling the client the Brooklyn Bridge or the moon".  The attorney does not have the offer to give.  The prosecutor makes the plea offer and the judge determines the sentence.  The criminal defense attorney should present to the prosecutor the client's truthful circumstances (in the light most favorable to the client).  Most prosecutors appreciate candor and will be more willing to negotiate with an honest and ethical criminal defense attorney who they can trust.