I've taken to fighting quick battles more often due to time recently, so what I do then is usually:
SIEGE:
Get melee and cavs to hold some distance in from entry point. Get archers on the towers besides the ladder and entrance, even better, crossbowmen. That has always worked for me. But if the castle does not allow this, just force a situation where your ranged troops can fire unblocked by shields and un-harassed at the Nords. So far, I've yet to meet a Nord who shielded above as he fought at the front lines.
OPEN BATTLE:
I really rely on ranged a lot, just line them up, distract the Nords with your other men, tada. Assuming you don't have them, depends on the calvary and infantry you have. Heavy calvary, let them rip. Light calvary, have them circle around if possible(By being cav yourself and getting them to follow), and hitting only from behind. Will cost you lives. Light infantry, I recommend sticking close to the archers, dashing forward and holding them off for a bit. Not a good idea to use light infantry, though. Heavy infantry, meattank while you send another group to cut them up from behind.
CLOSED BATTLE:
Be afraid. Be very afraid.