I guess making a best-seller is a two step process:
1. Give people what they want.
2. Tell them about it.
That's the simple part.
But first you have to figure out what they want.
How do you find out?
Well, you can ask them through surveys. You can study other best-sellers in the genre. Or you can give them your texts for free and see what people think about them. (That's the approach the author of 50 Shades took as well as author Scott Siegler.)
And how do you tell them about it?
By having a great cover and a description that makes people want to buy.
And by showing them your book, either because you were a clever author who build a list of subscribers. Or because you use social media. Or you pay for ads.
There you have it.
Oh, and story counts, too. More than grammar and spelling.
I just read this excellent article about it, in fact. It gets boring towards the end, but it's a valuable read:
When I was around five years old, I went with my father to work sometimes, and I always loved that they offered me a typewriter and paper.
That white paper... all those possibilities! A year or so later, my parents gave me a light-brown typewriter made out of plastic. One of those things that was made for children. With it I typed stories and fairy tales and used my imagination. Later I got a real typewriter (still not electric, though) and I kept typing. My biggest dream was to become a writer. High-school killed my imagination, but I discovered a new-found love for writing non-fiction. For several years, though, I almost didn't write. I worked in a bank for six month, studied medicine, worked in a supermarket, worked as a childminder, as a secretary and book keeper for a lawyer, before I finally dropped my day-job for good and started to write books. My books were non-fiction books, and they were published through a couple of Danish publishing houses. I also sold two short stories (out of the three I wrote) to two of the biggest Danish magazines. Until recently that was the only fiction I could boast about, because I struggled to write a novel. That's all over and done with, luckily. I grew up in Denmark (and Germany for 3 years), but in 2000 I left to live in France. We stayed there until June 2011, where my husband, son, cat, dog and I moved to Israel. When I write today, I have a view over the blue see, the blue sky and the ever-shining sun.