Do you shoot, look at histogram, adjust if needed, shoot, look again, etc? on every shot?
Speaking for myself, while I keep an eye on my histograms to make sure I'm not blowing out my highlights, or crushing my shadows, too much I don't feel the need to check it on every shot. But if you're still working on getting exposure down, check them as often as you need too. I harp on Histograms a LOT because they're an amazingly powerful tool.
One of my favorite tutorials on this is over on Photography Life:
Understanding Histograms in Photography
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If i were shooting at 1/500th ( to capture movement), iso 200, f/8 ( to maintain depth of field)- and the histogram shows too dark, which element would you commonly change first? and why that choice? thanks.
I shoot in Manual mode and enable Auto-ISO and here's why. Aperture and Shutter speed control not only two parts of the exposure triangle, they also control two very important
aesthetic aspects: Aperture controls the
depth-of-field and shutter-speed controls either stopping, or creating,
motion blur. ISO on the other hand, for me, is far less important because it has little or no aesthetic affect on my shot. Oh sure, at some point digital noise becomes an issue but that I can deal with quite handily during post-processing. Depth-of-field and motion blur I can't. So, that being the case, I want rapid, easy control over Aperture and Shutter Speed so I can rapidly and easily control what's important to me.
The answer to your question primarily depends on what's being shot and what you want to get out of the shot. Good photography is ALWAYS a juggling act of Aperture, Shutter Speed and ISO. You have to determine, in your mind, how you want the shot to look, and then you balance the different tools of exposure and composition to get that particular shot. Maybe I see the shot is a little underexposed but it has the DoF and amount of motion blur that I want. Can I fix the exposure during post? If I think I can, I get on with shooting. If I don't think I can, I'll have to juggle DoF, motion blur to arrive at a compromise I can live with. There is no single right answer to any particular shot and the juggling act will never, ever go away; it just gets easier and then it becomes second nature.