Serious conversation needs to be premeditated scheme. Do not start a conversation, not defined with arguments. It is also important to feel the time, do not rush things, give the other person to understand your description, and then move on to the next phase of the conversation. This way you can win without much difficulty former enemy on their side.
Of course, the big mistake is to start discussions or embittered spoiled mood. This gives an interview excessive emotionality, changes smooth flow of words and deprives the patient. This means that even a "killer" arguments will be spent in vain, because they will be used in improper time when the source has not "matured". In this case, the initiative will be lost, and the victory in the dispute would be highly questionable.
To at least roughly predict the reaction of the opponent to certain statements to reflect and prepare his counter, remember previous conversations, of course, if the person you already know. It makes sense to try to gently inquire about a new business partner, especially when in front of important negotiations.
Not only must convincingly and confidently express their thoughts, but also be able to present all the benefits of your options, ideas, projects, etc. for most of the interlocutor. It is desirable to reinforce this view at least approximate calculation. Thus you convince your opponent that is important to you is not so much to win in the negotiations as to show the benefits of a solution that will be beneficial also for him.