Here's a basic tip for early game SP or MP:
Keep at least one commander (an indie is fine) behind your army(s) of expansion. If you do suffer some sort of setback (I've often captured a province, but had significant portions of my army rout back the way it came before the outcome was settled), it will minimize your "downtime" before you can get offensive operations back on track.
Pause a turn to recruit reinforcements with your main army, while your trailing commander brings up the stragglers/cowards, and then you're back on the move.
Actually works best on those risky "line" expansions, as your routers have only one way to flee
