Orders:
When creating npcs that patrol consider whether they should patrol when the player is not watching. If you want them to patrol when the player isn't watching the documentation says to set bAlwaysPatrol to true.
Only looping or shuttle patrol paths are possible, but rather complex paths can be achieved just by using pathnodes to connect two patrol points.
When a sentry spots an enemy he'll leave his post to run off and attack. If you want him to return to his post when everything's back to normal place a guard point and give him 'Patrolling' orders with the guardpoint's tag as the orders tag.
Consider using the 'Crouching' order for snipers and the like.
AI:
bCower should generally not be set for armed NPC's.
bKeepWeaponDrawn is useful for patrolling enemies; ask yourself this question: Is this guy expecting to be attacked at any moment? If so, this property should be true.
RAISEALARM_BeforeAttacking is good if a guard is standing close to an alarm unit.
Combat:
bAimForHead raises the difficult a lot. Consider filtering any NPC's who has this out on at least the Easy difficulty setting. Alternatively, spice up an area by placing somebody with this on only the Realistic setting.
BaseAccuracy is probably one of the most important AI settings, it defaults to 0.2, and as far as I've been able to discern, 0.0 is max. If you raise this value, NPC's will hit badly, which is good for random thugs and other people who have just somehow acquired a weapon. 0.1 is good for more elite enemies. I think ZP has 0.05
bUseFallbackWeapons... I wonder if this works... if it does what I think it does, it should probably default to true?
Inventory
The following weapons have tnm versions and the originals should not be placed:
flamethrower
combat knife
sword
crowbar
assaultgun
gepgun
plasma rifle
