I just got back from chaperoning a high school trip to Costa Rica. While there, some of the kids put together a make-shift Diplomacy game out of a pizza box top. Playing gave the kids and me fun lessons in leadership and negotiation.
The rules of the game are very simple, but playing well requires players to negotiate alliances. Everyone has to figure out whom to trust and who will stab them in the back.
The simple approach is to make promises to several people and surprise one by breaking your word and attacking them. Too many lies and no one will work with you, then you lose. I was pleased that our team was able to do very well and never told a lie during a negotiation. I was reminded in this short exercise how effective truth can be in building good relationships. We told the truth even if it was only, "It's not in our interest to support you right now."
I'd recommend trying the game as a fun way to practice negotiation and to try out different approaches to working with people. Its a safe way to see what works best for you.