Usually I write on google docs but if you prefer in a Nb or looseleaf, and I just plan it out.
Outline:
Character Name:
Personality
A couple of bullet points.
Back story
One or more bullets.
And basically if the characters are opposite find a reason why they would meet or talk. Also I would suggest that you make the characters first, sort out the personalities and watch some tutorials or simply just test and experiment with some of the commands.