When it comes to writing either non-fiction or fiction, there is one thing you should always ask yourself....what's your point?
No matter what you are writing, you should have some sort of goal in mind - what are you really trying to get across to your reader? For non-fiction, most narrative essays will have some sort of moral to the story, some reason for telling the tale. And for non-fiction works such as term papers and other types of essays, there is always a main point to the paper. When choosing arguments, evidence, and examples for your project, keep your main point in mind...make sure everything you are writing supports that point.
For fiction, what is the main point of your story? What are you leading up to? When writing your scenes, make sure they are leading somewhere...there shouldn't be anything in your story unless there is a reason for it to be there. It needs to move the plot along, there needs to be a reason you are spending time depicting what you are depicting.
Just remember your point :)