This is something you can do at any point in the writing process. Figure out how everybody feels about everybody else. I was told this technique by Northrop Davis, and now I share it with you.
I started with my hero in the middle, and then worked my way out from there. Allies. Opponents. Major players. Minor characters.
Then write down the dominant idea, the main thing that each character thinks about the other character. And, remember, it goes both ways.
Creating this chart makes you realize, “Hey, these two have no scenes together in the story at all! Better figure out a way for them to have a bit of a relationship.” It is fascinating how drawing the chart triggers ideas. I invented new, and crucial, relationships because I drew the chart. I invented new characters. New situations.
It’s another way to jog the old brain into a different gear, and I highly recommend it.