There was an article posted on Facebook recently by CreateSpace, Amazon's paperback division, asking one question - what is the most important element of fiction?
I think it's got to be tension. Raymond Chandler once said When in doubt, have a man come through a door with a gun in his hand. Anton Chekhov put it another way; If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off. Both comments mean the same thing, that an author must keep the tension high.
Not that you need a gun. The romantic fiction genre survives on the basis of "she will, she won't, she does", as a woman dithers over whether to marry her lover. (Yes, I'm sure there are exceptions, but that's the general rule). Wuthering Heights is a tale of people caught in in their own tangle of love and envy, and destroyed by it, with nary a gun in sight. And so on; you don't need a list. The point is that tension can be created by any conflict, physical or emotional or anything else - but you do need conflict. Without it your story might end up like this;
"Fine, Bob. You?"
"Fine. Kids all right?"
"Not bad. Well, see you."
Tension comes partly from pace. The fashion today is for fast-paced tales, in which one event is barely over before the next is upon our protagonists. Look at The da Vinci Code as an example. It's not very well written in truth, with cardboard characters and a predictable plot, but it does rattle along at a very high pace. Sometimes that can distract the reader enough that he doesn't realise the book is a bit rubbish, the same way that big explosions do in some films.
But tension can also come from characters. They can lie to each other, betray friends, plot and scheme together against an enemy. Or they can be driven from their comforts and forced to embark on a journey they never wanted, perhaps to regain their former lives, perhaps to find themselves liberated. If we have the skill, we can create enough tension this way that we don't need a rifle hanging on the wall, or a man with a gun bursting in (Well, not very often).
The Harry Potter books are a case in point. In the early volumes - up to number four, The Goblet of Fire - there's hardly any clear danger until the end, and not much threat of it either. We all know the danger is coming, but it takes forever to appear, which creates tension for Harry and his friends, and by extension to the reader. And it works: for the most part the Potters are very tightly written indeed. I know it's fashionable to criticise JK Rowling these days - as it is to criticise Dan Brown - but in Rowling's case I think it's unjust. The realisation of the wizarding world is brilliantly done, and as Stephen King says, the books are also cracking good fun.
But you know. other people will have their own ideas about the most important element in storytelling. God and all the little fishes know there are lots of important things. Tension is only my choice. If you can make a story work another way, then good luck to you.