I've had alot of success as the Aedui, basically I disbanded the troops that I wasnt going to use and attacked the Arverni head on from the start, combining them into one big army. I took all three of the Arverni Transalpine holdings but lost my one Cisalpine holding to them, then I went about uniting the rest of Gaul and beefing my army up. By the time I had most of TransAplpine Gaul united, I had one big experienced stack, and the Arverni had been building up their forces, I attacked immediately before they could become a threat, crushed them, and eradicated their faction. Then, I turned back to uniting all of ancient Gaul proper and recently succeeded.

On the battlefield one big key to my success has been the use of Germanic mercenaries to make up the center of my line. In my experience, the Fraemarhajoz or however they are spelled are simply "better" at holding the center line then their Celtic counterparts due to their better morale and denser formation. My own Celtic spear armed southern infantry makes up the near flanks/outer center and my sword armed Celtic troops either make up the outer flanks or are positioned behind the center as sort of a "second wave". The versatile Celtic light calvalry makes up the far flanks for flanking/harassing manuevers and of corse to persue routers.