It depends. If you want it to be placed into the future or in the past, or even in the present. It depends on how complex you want the story to be. What kind of programs your using, or computer, etc.

For story plots you want to read a lot. Make the character's differ from each other. If you have a renegade main character, make some of the extra character's snappy, peppy, warm hearted, sweet, loving, etc. If you want a mysterious chararcter, do just the opposite to balance it out.

You want to have choices open in your story plot. To make it more dramatic make characters memorable. I usually like to read, take things relevant of the books story plot and incorporate it into my own story/game. I can't get into much details of anything else, because of such few information you have said.