Service Hardening

Hi All,

If I want to harden a server and/or PC so that only those ports, services and programs required form normal and emergency operations are enabled, how do I go about doing this (Particularly for services)?

I can retrieve a list of services running on a machine, but how do I go about determining which ones are required and which ones can really be disabled and/or removed. How do I know if a service may be required under an unusual circumstance? Step by step is appreciated.

We are required to do this to meet NERC CIP compliance. The CIP specifications state the following:
"R2. Ports and Services-The Rersponsible Entity shall establish and document a process to ensure that only those ports and services required for normal and emergency operations are enabled"