Since Clausewitz would contend that the purpose of war is to make another nation or people submit to your will. I will bring up people's will as a planning construct is important because it is the key terrain in an insurgency. What actions are you going to take make the local population neutral to passively friendly, and break the will of the insurgent. RTK posted alot of "how to" information. The key in using "people's will" as a COG for planning is that it helps drive and synchronize your CMO, IO, and security operations. It is tied to public perception and public opinion. As a military planner it is important because we try to avoid it and pawn it of on other government entities that either don't exist, or they are not resourced for it (state/commerce/IMF,UN,etc). Since the NGO's/PVO's/agencies can't do it, as a militayr planner I have to. I saw the shoulder shrug, hell I shrugged my shoulders, in May and June of 2003 when we had not factored people's will and how to win it as a planning construct in Iraq.