While publishing houses have staff editors who can organise and suggest improvements on a book's manuscript, if you are planning to self-publish you will have to do it yourself or hire an editor. 

Writing is a big job and it is not always easy to see the forest for the trees. An editor will look at your manuscript with an eye to organising the book so that it flows and makes sense to the reader.  They will be able to suggest to the writer where and how the book could be improved. As well they will ensure that the grammatical elements are correct.

As an experienced editor I can assist writers in developing and readying their manuscript before publishing.