One thing you need is literary tension. What the heck is this, anyway? Recall, in general, tension is mental, emotional, or nervous strain. I think the thing to keep in mind, however, is we want to evoke tension in the reader. Tension is the mechanism we employ to make the reader want to keep reading. We want the reader to wonder, "What happens next?"
Often in critique groups, it seems like tension gets a bit mixed up with conflict. Literary conflict is something different. Conflict is when something or someone stops a character in a story from reaching his/her goal; it can be an external or internal obstacle. The reader has to know what the goal is for this to work. I would say tension, then, is a result of conflict. The reader wonders, "Will the character overcome this conflict?"
How, then, do writers create tension? In a nutshell, the author has to evoke questions for the reader and not answer them right away.
how-to-evoke-tension suggestions from around cyberspace include utilizing:
- a mystery or puzzle--The classic here is, of course, a dead body or other committed crime that must be solved. But an author could also have a secret, a magic ring, locked treasure chest, etc. that the reader wants to find the answer to.
- a solution--The author tells the reader the end of the story and the reader wants to find out how the story gets there. A lot of thrillers utilize this, e.g. bad guys are going to blow up the world unless... Come to think of it, romances use this method as well: the reader knows the boy and girl (or whatever) will get together at the end, but how does it happen?
- Related to the solution is the author actually telling the reader things. I see this a lot in the beginning of (successful) books and stories.
- present hints and possibilities--Savvy readers know when an author spends time on a character or object it's important, e.g. gun on the mantle, suspicious janitor, etc. Readers wonder, "What's up with that? What's up with him?" This method could also encompass multiple plot lines or protagonists. Readers want to know how they all fit together. Plus, as an added bonus, when you change point-of-view it evokes tension in the reader: "Wait. What happens next with this first guy?" This can be tough to pull off in a short story, however--you don't want to get too complicated.
- knowledgable reader--Here, the reader knows more than the characters, often because of multiple points-of-view. The reader gets to see them all, but the characters do not. "Oh, no! That guy she's dating is the guy that killed her sister." :) Horror stories often utilize this. Readers know the characters should not go into the basement. Alone. At night. Bare foot. In her negligee. With a killer on the loose. In the house...