In a successful negotiation, everyone should leave the negotiating table happy with the outcome: there shouldn't be winners and losers.
The negotiators should try to reach a [?]: an agreement of equal benefit to both sides. This can be achieved in a number of ways.
One way of furthering negotiations is [?] (asking the right questions and listening carefully to the answers).
Through a series of proposals or offers from one side and [?] or [?] from the other side, the two sides work towards an agreement which will benefit them both.
Here are some ways of making offers:

If you offer more flexible payment conditions, then we will be able to (+ infinitive)
As long as engine performance improves by ten per cent, then we can agree to (+ infinitive)
On condition that you deliver 20 engines by May, then we could consider (+ -ing)
Supposing that you provide good technical support, then we may offer (+ noun)
Provided that you supply documentation in Portuguese, then we might offer to (+ infinitive)
Providing that this contract works out OK, then we could consider (+ -ing)

When you offer to change your position to one that is less favourable to yourself, you [?].
Perhaps this is in exchange for a [?] from the other side, although there is no guarantee of this.
Your concession may be a [?]: a concession that you make hoping that the other side will see this as friendly and make a concession in return.
Even in a friendly negotiation, there may be [?], with each side making a series of concessions in return for concessions from the other side.
(This expession is often used to show disapproval.) If you argue about something, you [?].
A series of concessions in exchange for concessions from the other side is a series of [?]s.
If you make a trade-off, you give something away and get something in return.