Here, in no particular order:
5. Your storyline is compelling
You’ve created a sequence of events that progresses logically and purposefully and that culminates in climax. This sequence is called plot. The plot of a short story can (and probably should) involve just one single incident or main conflict. And conflict is clash. A clash of what? A clash of desires. On the other hand, the plot of a novel — even a short novel — should be more complex and involve a series of incidents. This series should progress naturally, yet not predictably, and if your storyline achieves that, you have on that level succeeded in writing a good book.
4. You’ve given the reader something to be curious about
This is what I call a Thread of Apprehension, which is closely connected to the issue of suspense, which in turn is closely connected to the issue of plot. To create such a thread, you feed information gradually to your reader and you build a conflict which will in reason interest your reader. What do I mean by “in reason”? If, for example, your character’s big conflict is what color she should paint her toes and what her friends will think of this, you will not have a conflict of any universal appeal: your characters, thus, being people who are concerned with such things, will not have universal appeal either. When you create a thread of apprehension, ask yourself this: is there any good reason that readers should be interested in this clash? Are the desires and values of my characters important enough to be curious about?
3. Your climax resolves your central conflict
Chekhov’s famous rule — “Never hang a gun on the wall in the first act if you don’t intend to have it go off in the third” — compendiates this principle perfectly. (The breach of that rule, incidentally, is known as a “red herring.”) If you create a lot of genuinely interesting conflict in your story and yet can’t bring the conflict together in one culminating scene, your story will fail. One piece of very helpful practical advice a screenwriter once gave me: devise your climax first in your mind and then plot backwards from that, away from the climax, always asking yourself along the way: what sequence of events are necessary to bring my characters to this point?
2. Your characters are remarkable
Readers are interested in exceptional people. What is exceptional? Out-of-the-ordinary and accomplished in some way. People who through their own choices and decisions and effort of will have risen above the average — even villains. Two-dimensional characters, uninteresting characters, characters with no depth, or characters whose motivations are unclear or unbelievable — they bore us. Upon the other hand, characters who are in some way remarkable — and realistically so — grab readers and make readers want to know what happens to them. To create characters with depth, however, the writer of course must also possess a certain amount of depth.
1. You know why your novel was written
Too often, we read novels written by writers who think that a novel is a journal. Or a memoir. Or a chronicle. A novel is not any of these things. You can in your novel write about mountain climbing or marlin fishing or marijuana smoking or your youth, provided you show us in the work why there’s a reason we should be interested in these things. That reason is called theme. Theme is the meaning that the events of your story add up to.