Negotiation often has a negative connotation. Just the word: negotiating, 'getting the other 'under your hand'. There is then apparently a parent and a child. A winner and a loser...
Constructive Negotiation requires a different mindset as far as we're concerned
It assumes that you want to look for 'the common ground'. That you are curious how you can strengthen each other and not that you are looking to eliminate the other as quickly as possible or get as much as possible at the expense of the other.
Win-Win thinking plays a role in this. Solutions that add value for you and the other(s). Solutions that assume that they are more beautiful and valuable than the obvious solutions that are often found quickly.
It takes some time and attention to achieve a real win-win solution. Often we don't take the time to pay attention and it quickly becomes 'good enough'. Are you able to involve the other in a creative process that can lead to solutions that are important to both? Especially if you are forced to quickly arrive at an advice/solution/choice where the other pressures you to 'do better anyway'. Especially if the other is putting pressure on you to deliver quickly and where you feel that you may be overcharged. It is an art and a skill to arrive at such solutions.
I like this one even better and it's a level higher. Solutions that are important to you, the other(s) and the environment (several stakeholders, the environment, 'the planet'). In order to arrive at such solutions in which different parties, interests, risks, characters and views often play a role, it is important to arrive at a good approach in a structured manner, whereby you also sharpen your negotiation techniques.
In a constructive negotiation training you learn an approach (principles and process) and you are given a toolbox (skills and tools) to come to better decisions and deals together with others.
Learning to manage the relationship, the content and the process are central to this.