One of the sites I follow is William Beem who's mission is to provide other photographers with his experience and insight to help them change the way they think about photography. His recent discussion is Keywords vs. Collections and How to Use Keywords in Lightroom
When you're taking photos, you're taking photos of someone, a place, or a thing or event - period.
He uses a system he says that's been around for thousands of years.
.. Who – If my subject is a person, the name is added
.. What – If my subject is a thing, the related keywords go here
.. When – Nope, Lightroom reads the data information from your camera
.. Where – If my subject has a location, I add a keyword here
.. How – Details for lighting, cameras, post-processing, whatever (for yourself)
.. Other – Use it for whatever!