My advice is, stop when you've reached one third of map, build economy and loads of money. Then advance and try to keep as much money in the coffers as possible. That's all.
I had gathered something 40% of map, and had massed over 300000 florins. You know, it wasn't enough for 90% of the map, at this time I had to disband 10000 florins worth of upkeep of troops. Not something you feel like doing, but had to. Then again, they had already served their purpose, I still got a lot of men left, and it just showed how flexible leader I am