Few writers are good enough and few readers perceptive enough to keep track of more than three characters at a time. So if you have more than that — especially if you have a large cast of characters — group them into no more than three groups. That way you and your readers can keep track of them.

Three. Just three. No more than three individuals or three groups of individuals per scene.

Of course, in those scenes with three or fewer characters, you can forget the grouping and concentrate on the individuals. And that’s when you can round them out with unique personalities.