1.
We write a book.
Why do we write a book? Because a notion bestseller usually refers to books, at least in the nearest beyond-the-fence and beyond-the-screen lands, and if so, then the word badseller, which rather can not be found in a dictionary, should refer to books, too.
The plot, topic, subject are not really important. A book about nothing would be the best. Or the book with no topic, no plot, no subject. Yes, a book of this kind would be interesting only for a few. It should be written beautifully, stunningly beautifully, poignantly beautifully. Despite confessions and declarations not all people are fond of beauty, hence the reduction of the number of buyers, we can be quite sure of that.
Let’s repeat: we write a book about nothing and breathtakingly beautiful.

2.
It would be nice to write this book in a language known to nobody. So also to the author – that’s very important. The author would not be able to read what he wrote, so nobody would know what the book is about.
It looks excellent, but it is not excellent, indeed. There are always people for whom deciphering this unknown language, and this book, and let the author know what he wrote and how, whether he created a masterpiece or a scandalous pulp fiction, would be the most precious aim of their lives. The number of these fanatics will grow, they will found secret societies, public institutes, research groups, while the book will become an object of adoration and cult. Not nice.
Not nice not necessarily means abysmally especially when combined with the first paragraph. The hidden fans themselves will take care of their elitism.
Well, in fact language is not important, either. A book can be written in any language, even in a very popular one, provided that illegibly.

3.
A book should be written against a reader. Let it discourage a reader deliberately and purposefully. Let it make a reader scramble through thorny thickets. Let it contain barren lands and burnt waterless deserts. Let it have jungles full of venomous snakes. Let it make reading in a bath tube, on a beach, even in a comfortable favourite armchair impossible. Let it be constructed in a way to make you deeply confused when opening it and helpless when you want to shut it down. Let it be a labyrinth with no exit hence one would enter it under the threat of death and madness. Of course, there are always fans of extreme reading, but they are not the target for such a book. This is not the revenge of a tormented writer. This is to be a triumph (not right word it is, but let it be, the point is to gain some advantage) of semantics over aesthetics: we assume that every element, the tiniest part of the book is meaningful, so one has to read it simultaneously on many different levels, an ordinary reader is not ready for such reading, even among extraordinary readers there are not many who are ready... Not many readers. A few readers – this is exactly what we need. Only the number of odd-thing-collectors is a matter of concern.

4.
The price should be both too high and too low. Too high for those who really would like to read this book, posses it, keep it in their library to have a chance to come back to it in any moment. Too low for those who think price is the real value and who are ready to pay a fortune for something as valueless as a watch with diamond hands turning stupidly on titan pivot over the platinum face...

5.
We should not promote it specially. It’s enough to inform it has been released, it can be bought here and there. Let them look for it. Those who desire to buy it they will find it sooner of later. Provided they will learn about it. The overwhelming majority will not look for it, because they will be too lazy and they will know nothing about it. And that’s the point. This is the next sieve for readers and buyers.
Promotion – what should it look like?
DO NOT BUY THIS BOOK BECAUSE IT IS UNREADABLE.
Something like this?
No. This would be too easy and could have really regrettable consequences.

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