You can pick one of four nation groups, Yellow, Red, Green, Blue. At the start (and later on) play with historical picks. The important thing to remember is that you are playing a group of nations rather than just one,
There's a number of scenarios to choose from, but I normally play the first one, collapse of the Roman empire.
Red- Romans, Franks, Catholic Church, Irisk
Yellow- Sassanid Persians, Blemmyes, Britons, vandals
Green- Huns, Arabs,
Blue- Various Goths
Start with something simple like Yellow- Persia's not too big, you can build some decent armies
The nations you play change as the game goes on. Some events are scripted, others are random.
The main advice I will offer-
- As a barbarian, you only control the area your armies are, so after a while you will suddenly not control a lot of territory. Don't be worried.
- You're playing a group of nations, not just one. If one dies, you keep going with the others.
- Recapturing rebel held territory is extremely important (less aging)
-No point building improvements on fought over territory, they just get burnt.
-Only a few buildings are profitable, mainly farms, mines, granaries and markets. Most others are only profitable if there's a resource present (e.g., wood for shipyards).
- Use your strategy cards wisely, to win key battle etc. The AI uses them in a somewhat scattered manner.