I am first and foremost a lover of Rome. But, once you beat the campaign, you must move on.

When I'm not playing Rome I like to stick to the phalanx-based factions because they are almost impossible to beat. My strategy when playing any of the above factions is to have 1 archer (not peltast/slinger) per 2 units of infantry. I always use fire arrows to frighten the enemy and let them come to my spear points. There's no sense in moving phalanx-type units because they break formation and drop their spear for a sword. I don't bother flanking, unless it's possible because my massive line of infantry just happens to be bigger than theirs. I battle through attrition. Cavalry, with these factions is a complete waste of time. I use my General (when mounted) to chase down and slaughter fleeing enemy units so as to prevent the army for staying on the map after the battle.

For those who rely on horse archers, etc, I simply avoid battles with those types of units, hide inside my towns since cavalry can't take walls, or throw full stack armies at them and let the AI control my other armies in a "hammer and anvil" maneuver.

Additionally, when my tech gets up to the required level, siege engines become a mainstay of my armies. When going on the offensive, I keep 5 units of anti-personnel artillery pieces, with 10 units of my best infantry, 4 units of archers, and my general. When taking cities, I substitue all anti-personnel artillery for anti-wall artillery. The chaos and utter destruction caused by these engines is absolutely undeniably awesome and also can eliminate 1/4 to 1/2 of the enemy before my archers weaken them even more. Again, I'm all about attrition. For fun, I'll send in the elephants if I have them (only when I've got tons of money to spare) to start the battle. If they're killed, oh well. If they run amok amongst the enemy, awesome. And, well, they'll always slaughter hundreds of them regardless.

Just to break it up, I play the barbaroi from time to time. When fighting against another tribe, infantry attrition to the death is just fine with me. Archers when available can always sway the tide of battle quite heavily. When fighting professional armies of the game's powerhouses requires a change in tactics. I like to use lots of ambushing and heroes to turn the tide. Flanking is a must, as surrounded units will almost always rout and be killed to a man. Chariots can be useful if you "cheat" and just drive them through an enemy unit instead of engaging in melee. Usually, however, to win with barbaroi, you are required to blitz and overwhelm through shear numbers.