Welcome!

I'm pretty much in the same boat as yourself, I've only ever completed a single campaign in BI, this was a Roxolani one on VH / VH I think.

As for attacking, well in my opinion this comes naturally For example, study an enemy's unit positioning, look for weaknesses, then with a cavalry unit in wedge formation, punch a hole through the enemy's lines. Bring up your heavy infantry quickly to exploit this breech your cavalry have just made.