The largest thing that helped our agency was a few VERY good medics, and our very high level of communication. I would later join up to another relatively high agency, but they simply were not as good, partly due to the fact there was little communication.
Also we were not allied with any of the top teams, or any member of their alliance which cost us third place more than once.
Communication and good medics (and assaults for that matter) are essential, indeed.
Hehe, AvA is like that, at least half the battles are won in the chat. My agency was allied with Mercenaries, Red Alliance and MESA. Hopefully I don't have to explain who they are.
That has very nice benefits of being able to trade hexes that we didn't need for the ones that we did need and not being the primary target of all Top 3 agencies is a nice perk as well.
I never participated in diplomatic battles though (only with Red Alliance, they talk crappy english and no one but me in my agency talked Russian), every time our leader made a peace treaty with some scrub agency, like iCUGaming (lol) I would get disappointed because there were one less team to smash this season.