Begin with the relationships in the frame
Black and white can bring attention to the contrast between light and dark, the line of a shoulder or the way two people occupy a space. Look for a photograph with a clear structure before reaching for a monochrome treatment.
Keep a range of tones
Deep shadows and bright highlights can be expressive, but a picture needs room between them as well. As you edit, look at skin, fabric and background separately. Preserve the details that help the image feel believable rather than pushing every photograph towards the same dramatic finish.
Choose with intention
A colour photograph is not automatically improved by removing the colour. Compare both versions at the size you intend to use. Ask which one makes the subject easier to read, and let the answer vary from picture to picture.