Unfortunately I can't recommend any book, though I wanted to give some examples of leadership b-schools look for:

Taking initiative:
- Suggesting ideas in a project and implementing them
- Improving a process to make things more efficient
- Founding a club, organization, or non-profit
- Being proactive and following through with ideas

Then there are the common leadership examples:
- Leading teams at work
- Leading teams through extracurricular activities / non-profits
- Military experience

Hope this helps.

You could also use volunteering experience as an example of leadership. For example, in my applications, I could have provided examples from work, school projects, research that I have conducted through a lab. However, all of this came back to my career or research related to my career interests. Therefore, I decided to use my volunteering experience - helping students with reading skills - as an example of leadership. I believe that using a more unique example can help you emphasize an unconventional background or interests.

Good luck.