Doing some studio work certainly taught me a lot about using natural light. I'm usually thinking of the sun as the "key" and either moving myself or the subject so the light is where I want it, or if the subject is immobile like a landscape--waiting for it to get into the right place or for the clouds to work themselves out to the advantage of the scene. My favorite light is just after a rainstorm where there are heavy clouds and clear sky with sun breaking through. Anything looks interesting in this light.
I do like to revisit locations in different light and see what I can make of them. I'm always photographing this great view from our apartment, and I've learned a lot by doing this. There's a point at which the sun just gets up over the buildings on the left of the frame to light up the tops of those trees that's really nice, especially in winter, as in the shot above. If I'm shooting color slide, I meter the highlight side of Grant's tomb and close down 1.5 stops. If I'm shooting large format transparency with a lot of front fall and a wide lens, I know that the falloff at the bottom of the frame will be significant, so I'll try to wait for the trees in the foreground to be brighter than the rest of the frame. If I want Zone V when the trees are leafed out, there's one that's a little lighter than the others that functions as a good Zone V.
One of the main attractions of the zone system, BTZS, or development by inspection to control contrast, is that this kind of control over exposure and development lets you shoot intelligently under a wider variety of available light conditions. I'm always amazed by Adams's successful images that were made under "bad" overhead midday light. He just seems to find the place to stand where it works compositionally and then uses contraction development to keep all the tones on the film.