"Every period of human development has had its own particular type of human conflict---its own variety of problem that, apparently, could be settled only by force. And each time, frustratingly enough, force never really settled the problem. Instead, it persisted through a series of conflicts, then vanished of itself---what's the expression---ah, yes, 'not with a bang, but a whimper,' as the economic and social environment changed. And then, new problems, and a new series of wars."
~Isaac Asimov (I, Robot)
When I first started thinking about this topic, I considered approaching it from a basic level--discussing the main types of conflict (Man vs. Man, Man vs. Himself, etc.) that usually get touched on in high school and college literature classes. (If you do need a quick review on conflict types, there's a Wikipedia entry you can view by clicking here.) Instead, I want to discuss how you can take this information and practically apply it to your own book or series.
1) The degree you use a certain type of conflict may depend a lot on your genre.
For example, romance novels tend to deal heavily with internal and interpersonal conflicts while thriller/disaster books rely more on characters responding to external forces they can't control. One thing I love about writing sci-fi is the opportunity to use a wide range of conflicts, and something that can add uniqueness to your work is introducing conflicts readers may not typically expect.
2) Draw upon your characters and setting for initial conflict ideas.
If you have well-developed characters with varying personalities, you can find opportunities to create tension between them even when they're allies. What are your main characters' greatest strengths and flaws? How could their traits impact the overall story?
With setting/world development, you can have both natural conflicts (storms, earthquakes, etc.) and cultural conflicts (political and social issues). Like characters, setting can be a lot more interesting when conditions aren't perfect.
3) Use history and current events as prompts.
Most of us are bombarded by news on a daily basis, but this can give you an opportunity to take topics that interest you and explore the related conflicts in a fictional environment.
I've honestly just started doing this myself, but keeping an ongoing reference file with headlines and news story links could be a helpful brainstorming tool.
4) Stage your story's conflicts before you begin writing.
With my own series, I started out with the major conflicts (ones that carry across several books) and worked my way down to smaller conflicts that may be resolved over the course of one or two chapters. You can do this in an outline or even a storyboard--the main point is to have an organized plan on where you are and where you're heading.
Beyond keeping a reader entertained, conflicts have purposes. You can reveal what your characters are like under pressure and contrast them with other characters. Internal conflicts give you an opportunity to show a character's personality through action and his/her thoughts as opposed to just telling the reader about them.
5) Chapter structure impacts pacing and tension.
Once I establish the conflicts in a particular book, I alternate between them--ending a chapter on a moment of tension then picking up the next chapter with a different set of characters and conflict. Even as readers are focused on reading about one conflict, they're concerned about the others.
6) Give readers a reason to care.
Have you ever watched a movie with great special effects but no character development? The moments of tension are lost in the fact that you could walk out of the theater without the slightest concern on how it ends. The same concept applies to books. If you open your story with an action scene (which isn't a bad thing), follow it with an opportunity to know your characters better. There is a balance to it, and you can learn a lot from observing both stories that do it right and those that do it wrong.
I appreciate your time reading this and hope you've found these tips helpful. As always, if you have any questions or are another writer with a different perspective to add--feel free.