COST:  

How much can you afford to tie up for 2-3 years?

CUSTOMERS: 

Where/how will you find them? 

CREDIBILITY: 

Do you have the background and experience to write about  this subject? 

CONTENT:

Do you have enough content for a book?

COPYRIGHT: 

Have you held onto the copyright for work of your own you want to incorporate?

CLARITY:

Do you have a clear vision of how the book should look?

Do you have a clear idea about how to sell it?

CREATIVITY:

What sets this book apart from others in the same genre?

CHRONOLOGY:

Do you have the time to bring this project to completion within a reasonable time frame?

Are the key people you need to work with (production manager, designer, photographer, 
researcher, professional editor, printer) going to be available when you need them?