Maybe another tack...

The old Kodak recommendation was simply, "If your pictures are consistently too contrasty, reduce development time; if they are consistently too soft, increase development time."

With roll film it is almost impossible to not have scenes of different contrast on one roll unless you use dedicated backs or camera bodies. The thing you want to achieve is a "standard" developing time that allows you to be able to print all those different-contrast scenes on the grades of paper available to you.

When I shoot roll film (which is rarely these days) I like to find a developing time that allows me to print a "normal" scene (think hazy sunlight with open shadows) on grade 3. Then I have enough leeway for more and less contrasty scenes.

You do need to develop a sense of how contrasty the lighting is (soft vs. hard as mentioned above) and where to expose, but that's pretty basic. I recommend to in-camera meter users to use the meter's reading for all cases except when the subject is contrasty. In that case, the meter has a tendency to underexpose the shadows, so open up a stop (or use the +1 stop exposure compensation) for contrasty scenes.

Do that and find a good standard developing time for your style and type of work and you'll be just fine. I'd start with the manufacturer's recommended developing time and then alter that as needed, using "If your pictures are consistently too contrasty, reduce development time; if they are consistently too soft, increase development time" as a guideline.

Best,

Doremus