The moment you transform your expression in form of book, poetry or the like into piece of paper it become copyrightable. The copyright is by default once the work is fixed in any tangible medium of expression like if it is reproduced in the piece of form or even recorded via digital medium, i.e. recorded on hard disk of your computer. Though the registration of the copyright is not mandatory under the Copyright Act, it is advisable to get it registered. However it should be noted that even if the work is registered and your work is entered into the register of copyrights, it would only be primafacie evidence that you are the owner of your work, that is to say the opposite party can rebut your claim by presenting stronger evidences proving his ownership. Thus, you can do the following:
In case of manuscriptt of the book you can get the work registered with the copyright office
Give the manuscriptt of your book with proper copyright notice to the publisher that it is your copyrightable work and no part of it can be reproduced in any form whatsoever without your permission.
Keep the manuscriptt of the book or work safe and along with the sources from which you created the same. Keep the same stored in the hard disk of your computer.