One of the differences between an ordinary, or even a good, novel and great one is that the former confines itself two a narrow scope and view of life, while the other offers a wide view and does not stop at the first layer of the story which is the immediate events. 

How to do it? Write the story with the narrow scope and then try to tie it to a wide prospect. Try to make it more global, more universal and maybe you may make it become even cosmic. 

Example 1: An ordinary crime novel starts with the crime and ends finding the criminal. If you write it well and have a big publisher, it may become a bestselling. But it will not survive for a long time and people will forget it soon.

Make it a great novel by embedding it into a philosophy, or at least a view of life. Tie the crime to a view of Life and Death, Morals, the Struggle of the Human Kind for A or B...etc.

Example 2: Here are three levels of writing a novel about a young man addicted to  drugs:

Level 1: The young man’s  friends try to rescue him. They find the one who sells him the drugs. Adventures. Chasing. Troubles. And they are successful. This is a novel with a narrow scope.

Level 2: Its view is wider. All the above until they find the one who sells their friend the drugs and when they consider the seller to be the only wicked man, they discover that he, too, is a victim and only a ring in a big chain. The great boss is their friend’s father who abandoned him and his mother ...etc.

 Level 3: Same as Level 2, but with adding the fault of the modern society which its greatest criterion is wealth. Such society is not a poor-friendly, turns a blind eye to faults of the humans as long as they are rich, pushes the humans to rush for wealth and power...etc.

Example 3: A short comparison between Carmilla, by Joseph Sheridan Le Fanu, and the famous Dracula, by Bram Stoker. It seems that Dracula was inspired by Carmilla, but Dracula is an example of a wide view. Carmilla occurs in palace in the woods some distance from a town. Although the castle of  Dracula is more isolated, but the stage of the events is the continent and it extends outside it; Britain. The characters fight Dracula there and then chase him back to his castle. But it is not only the stage, it is also everything: Dracula producing a generation of vampires; something like a holy alliance between the characters to defeat the monster; their fear and anxiety about the future of their country and the humanity. And while Carmilla, the vampire, appears somewhat suddenly, the roots of Dracula go deep into the history of Transylvania. Dracula was the leader lived hundreds of years before the events.

Disliking the narrow prospect, I found myself extending the horizon of my novels. In “The Warlock of the Village,” the young shepherd dreams of wealth, but I would not let him get it and live his life as rich man of the village. He leaves the village and comes back as a warlock, wealthy and powerful. But this should not be the end of the story. There must be an inner struggle, questions about life and death existence. And in “A Murder in the Cretaceous Period,”  it is not an ordinary crime or detective story. It is about the fake life of the human being, his fate, the disastrous effect of the powerful people. Even in the “The Bigs and the Littles” which is about infidelity and family life, there is a higher level of values: The bigs (adults and governments) lie to the littles (children and citizens).

So, when you write your novel, try to extend its horizon and view to life and existence beyond its simple story. That is the first condition for a great novel. And whether it sells or not, it contains great values.