Sit in on a light metering, film-making, Q&A training session.
First, a one-minute primer on the two ways a light meter can be used (via In Depth Cine):
Robert Machado creates a case study and Q&A in Light Meter Basics: Understanding Lighting Ratios, to demonstrate and take questions on his techniques in applying contrast ratio concepts in real shooting scenarios:
Rob Ellis goes through, step by step, how to use contrast ratio to achieve a scene which looks dark, but also looks correctly exposed…
… and, in the process, reveals how, contrary to what one may expect, noise in the shadows can be reduced if lit for a lower ISO:


Further Viewing
To learn more about the concepts Robert references, here’s a roundup of explainers and tutorials on contrast ratios:
And here’s a more detailed look at specific tools to help nail exposure and contrast: