Advice to would-be authors
How do I write a best seller?
What makes a best seller? Great ideas, in a good style, that loads of readers will benefit from reading. Can your book's subject be encapsulated in a title that is so obvious and catchy that bookshop browsers will reach it down off the shelf? You also need a publisher who can get your book onto lots of shelves. My advice is that you should try publishers with great distribution and sales organizations first.
There is also an element that best sellers are published at the right moment in time. Few (if any) bad books become best sellers, but lots of great books sell in only modest quantities. No one in the industry knows what is that magic alchemy between a book and the readership, at a particular moment in time, that causes the market to gobble a book up.
I have read books that explain how to create best-selling concepts for your book. Unfortunately if you are a potential author it's probably because you have something specific you want to say, and you are driven to write it down. It's just luck if the book you want to write will sell well. Read Rachael Stock's book on getting your book published, and then pitch your book to potential publishers - this will tell you whether you have stumbled onto a publishable idea. If you realize that your book isn't publishable, then think whether you can bend your ideas to write something else that interests both you and a potential publisher.