Before you submit your manuscript to a publisher, or better yet, before you begin writing your book, sit down for a minute and consider the potential readership. Ask yourself who you think will most likely want to read this book. This will influence the tone and direction of your book. For example, if you are writing a book about Kabbalah, we all know that you're not the first or last person to do so; there are a plethora of Kabbalah works out there on the market. You will need to provide a fresh perspective on the subject in order to make your book stand out from the 150 other Kabbalah manuscripts on the publisher's desk. If you are writing about a subject that requires specialized knowledge, but want to target your book to a wide audience, make sure to explain and define any complex concepts and language.
It is the publisher's and submission editor's job to weed out those manuscripts that are cliched and lack originality. They will only take on your book if they can identify a potential market, and unless your writing is of an excellent literary standard, your manuscript will gather dust on their desks and will eventually end up in the garbage.
One final word of advice: you never get a second chance to make a first impression. Your first page, your first paragraph, your first sentence, needs to grab the reader. Don't expect the reader to persist through 100 pages of waffle to uncover the point of the book. From word go, you need to engage your readers.
On that note, I will get back to work.