The key to effective negotiating is to understand the psychology of the process:
1.Know your bottom line
2.Aim high
3.Find all the variables you can
4.Get all their cards on the table before you begin negotiating
5.Never give concessions--trade them
6.Agree to all or nothing

Rules:
1 Let people feel they have squeezed more out of you than you meant to give
2 Agree an outcome that works for everyone
3 Look at it from their side, while you are preparing for any negotiation, spend a few minutes pretending to be the other person

Know your bottom line:
you must decide the point at which you would abandon the dael
you need to decide which factors are the most crucial
if you have no bottom line, you are not in a negotiation

Keep your bottom line to yourself:
do not tell the other person what your bottom line is
The bottom line has two main purposes:
1 it prevents you leaving the negotiatiing table worse off than if you'd never negotiated at all
2 By knowing the point at which you would, in theory, abandon the negotiation, it becomes far less likely that you will ever have to do so.

Aim high:
The other thing you must establish is your starting point.
The next question is, how high should you aim, and the answer is very simple: what can you justify. find evidences
Remember: what goes down won't come up

Never give concessions--trade them
you should do a deal on every point, do not give concessions, trade them. respond to every demand with i can only do that if...
this has two important benefits, the first, crucial advantage of this approach is that you end up with you need
the other advantage of this approach os psychological. you have shown the people you are negotiating woth that they are going to have to earn concession from you.

The lesson is : do not agree to anything until you are ready to agree everything