Negotiate is dificult.
It demands preparation.
Demands you to know more than the other side.
Demands you to understand what motivates negotiation of both sides.
A common error is to focus only on your side.
Be prepared, this is the secret. Do not enter a negotiation without knowing your goal.
Mainly if it is a negotation that worth closing or not.
"Failure to prepare is preparing to fail." - Benjamin Franklin