Yep - what Gilrandir said.

I NEVER train a single unit of peasants in any campaign, unless I have a severe emergency and no other choice. I generally use spearmen for 'bulking up' numbers, because they at least have some combat role.

They say it works especially well if you play the Northumbrians in VI and keep the bulk of your army in Elmet.
Exactly - this is my strategy for running a Northumbrian campaign - weak border garrisons attract weak invasions which are easily repelled, strong border forces invite a strong invasion... I did a long post in the Guides subforum about this for Northumbria.

+1 for spies and high-dread governers. Also religious buildings, town watch etc which add to happiness. I also tend to build only watch towers and not border forts - the happiness boost is the same, but border forts tend to catch all the enemy spies and assissins. Without a border fort then your own agents get the credit for the enemy agents caught, and valour up quite nicely....