I. Make an outline

I hate traditional outlining. I think lots of people found it hard to deal with during those teacher-enforced research paper projects in school.
Still, we need organizing tools when we write. I tend to use spreadsheet software to keep track of my characters and events in longer fiction. Kira Brady has another approach.

How to Plot a Novel: The Plotting Board Method | Kira Brady
http://kirabrady.com/2012/09/24/how-to-plot-a-novel-the-plotting-board-method/

A higher level of difficulty

Occasionally we read a story with a disabled character. The first one we meet may be Captain Hook. Ahab, another sailor, lost a leg to Moby Dick.

How does a disability – long-term or temporary (think “Rear Window”) – make a difference in a character’s behavior? What does he or she do to compensate? To overcome? To forget? What does he or she add to your story’s tone?

This piece points out some advantages to consider before you discount adding a disabled character.
Hiring Employees With Disabilities | Entrepreneur.com
http://m.entrepreneur.com/article/231731