Using a CPL...have questions

So I bought my first CPL and wonder if you pros have some advice on how to properly use it.

For instance, on a nice sunny day with blue sky should the CPL be rotated to get the brightest, clearest image in the viewfinder as opposed to the darker color when the filter is rotated? I'm just not clear on the proper way to do this.

Also what about on a cloudy day? Is the CPL even necessary if there isn't some specific glare issue like water or the like?

I'm sure there are many situations I'm not aware of and probably differing opinions but this should be an interested discussion.

For darkening the sky, just turn it until you get the effect you want. Its personal preference. Just remember that if you're using an ultra wide angle the polarizing effect will vary across the sky. This is normal and not a defect in your camera, lens, or polarizer. The effect is at its maximum when the camera is 90 degrees to the sun. With an ultra wide FOV, you're taking in so much sky the this becomes more apparent than it would be with a longer lens.

Just play with it. Youll figure out where you like it used and where you dont. Really isnt anything that says you need one for any situation. Its a tool and a preference.

They work wonders on removing glare from surfaces; green vegetation, glass, water, metal roofs and the such.