Write from passion and don't edit before you're done. Every truly inspired novel comes from a place of great passion. Even a regular person with no money, no connections and no celebrity status has a chance. If you are born to write, you will already be writing. Nothing will stop you. If something inspires you to write the novel of your lifetime, and you happen to have hit on something a majority of readers are into at your time in history, then your novel has a chance of becoming a bestseller. Of course, you will need to find a publisher who will give you a shot.
Write about an outrageous or taboo subject. Writing about things everyone thinks but no one wants to talk about is a good way to lose a lot of friends or sell a lot of books. If you happen to have talent, and a very original style (think Chuck Palahniuk, "Fight Club"), your book could get optioned into a star-studded movie.
Have a novelistic style or group of characters that can be serialized into many subsequent books. V.C. Andrews, J.K. Rowling, John Grisham and John Irving all have a breezy, signature style that keeps people picking up their books. People will buy for the brand of novel these people produce, regardless of the subject.
Have a huge bank account. If you have a large amount of money to market your novel, you have a great chance of becoming a bestselling author. Promotion and publicity will get your novel in the public eye. P.T. Barnum said it takes people eight times of seeing something before they start to wonder what it is and gravitate toward picking it up. You'll need plenty of publicity to be seen eight times by the general public in advertising and promotion.
Be a celebrity. If you are a household name and write a novel, you have a much greater-than-average chance of having your novel be a bestseller. People buy name brands. It's no different in the world of writing. Think Arnold Schwarzenegger being elected governor. Is he a great governor? No, but he was a great "Terminator." People knew his name.