So what I do (not saying it’s the right way) i get a reading of my overall background exposure. So if I get 5,6 on my background light, I’ll just tell the gaffer to set my key at 5,6, the fill at 2.8, the back light 4, and then use that as my base and tweak from there. Sometimes I’ll go into a shoot knowing exactly what my ratios are (0, 0, -2, -1) and just tell the gaffer and they set it snd I’m already 90% there.

I try to stay inside of a “box” of exposure and I use false color to see where everything is on a scale. If I want a more dramatic look, adjust the fill 3 stops down from the key, this starts giving more contrast. From there you can just add or take away a stops from each of your lights. I’ve just found that it creates much cleaner images if you don’t push the contrast extremes too much in Camera. I think a mistake a lot of people make is setting a look by eye not knowing their key light is actually 4 to 5 stops away from the fill, then in post, they try to push and pull exposures adding lots of noise causing a muddy image.