Conflict. Has a bad rep. because fighting, struggle and harsh words can be nasty in our real lives. But they are the lifeblood of fiction.
However, the definition is broader than used in every day conversation. Conflict occurs when your protagonist is stymied by people who don’t share his goals or by events/things which throw him off course. Doesn’t have to be ugly although it certainly can be if your plot calls for it.
Your main character might be thwarted by others who are sympathetic to his goals but, for their own objectives, need to prevent his from being achieved. A father wants to protect his daughter from getting involved in the murder, so he lies to the detective about her whereabouts.
Or a catastrophic, unforeseen, but nevertheless credible bolt out of the blue derails his plans. No Deus ex Machina, please, but sometimes Things Happen. A blizzard prevents the hero from seeing the cliff edge; the critical key falls down a sewer grate; a traffic accident throws off the precise timing of a heist.
How to write conflict into your stories
If your plot is working, then you probably have incorporated conflict into it. But just as a double check, review these points. Sometimes, it’s worth expanding on one or more of these points in your novel to strengthen it.
Response to a threat
Again, doesn’t have to be big. A student fears failing an exam which will prevent him from getting into a good university. What does he do in response? The threat usually occurs fairly early on in the story. Leaving it too late leaves the reader wondering what the novel is about.
Fight for the goal
Good fiction characters are fighters. They know what they want. When they run into trouble or are foiled, they take action.
So, this precludes writing passive characters. That is, a main character who mainly stands on the sidelines and wrings his hands about the antics or misdeeds of those around him. A narrator telling the story (see Stories in a Frame) qualifies as passive but is not usually the main character. The protagonist is usually found within the framed story. And if he is a good one, he’s in there swinging.
Conflict, not bad luck or adversity.
Bad luck, like falling out of a tree, or adversity, like being born poor, do not, in and of themselves constitute conflict. We’re looking for a fight between opposing goals. Bad luck or adversity can be complicating factors on the hero’s way to her goal but need to play a supporting role rather than been the star and center of the plot.
As I say, if your plot is working, this is probably more of a chance to see if any parts of your story need beefing up. But if you are just starting out, these are good things to keep in mind.