Take the book and print it out on paper for proofreading.  Then, starting with the last page and moving backward, use a ruler to look at each line in the book.  This is a tedious process and one for which you can pay a freelance proofreader.  You are looking for spelling mistakes as well as mistakes in punctuation.  When we read, our eyes naturally gloss over words that we are familiar with and often do not see that they are misspelled.  This is why it is important to take your time and proofread your book from finish to start.  By going up one line at a time, you will not be reading, but looking for errors that your eyes will ignore if you simply read the book. 

You can hire a professional proofreader for this purpose.  They will go through the book the way that suits them and deliver you a product that has changes.  They will put proofreading marks on your paper of which you should be familiar.  They will not make the changes for you, but signal you to make the changes. 

It is vital that you proofread your book or have someone else do it for you.  If you have a book published by the traditional publishers, this service is done for you.  If you are self publishing, however, you do not have this luxury.  

Proofreading a book is not like editing a book.  Copy editing is a completely different process altogether.  You can choose to copy edit your own book or have the company that publishes the book for you do the job.  We will discuss editing for your self-published book later. 

If you decide to proofread your book yourself, take your time and do it correctly.  Do not rush through this process as an array of misspelled words in your book will make it look less than professional to the reader.  You want your book to be as professional as possible so that the reader will not get turned off.  You can keep it free from typos, punctuation and spelling errors by doing careful proofreading or hiring someone who you can pay to do the job for you. 

Even if you have someone else who is not a professional proofreader take a look at your book you can have a fresh pair of eyes look at the book so that they can see errors where you cannot.  Remember that you have a very strong connection to your book that others do not.  You have most likely read it over and over again.  Having someone who has not looked at the book take a look for errors can help you out tremendously.  Most professional proofreaders will charge by the page.  This may be an investment that you will want to make if you are serious about making sure that your book is error free. 

Remember that even books published by the traditional publishers have errors.  Having one error in the book is not the end of the world.  Having a  book full of errors, however, can make your book look shoddy and not well put together.