1) I was wondering how many single out the enemy general for special attention by archers/artillery. That is, if he's in range, do you order them to fire at him?

I almost always target him. The less time a battle takes, the fewer casualties.

2) Do you use your own general in combat?

I always put him into the fight if the enemy is about to break.

3) Does anyone know how to improve the Natural Leader virture up to Fine and Great?