I'm in a bind as its my first attempt at a longer story. I've never had a problem keeping hold of a reader in a short piece because you can hit them with plot points and foreshadowing in a much smaller space. This slow-burn writing isn't coming easy, I feel like I need to get to the next explosion of interest as quickly as possible and my motivation suffers for it. I've had a plot in mind for a long time, with many major plot-points organised in my head and the core of the story sorted, but how I fill the weeks/months/years between these moments is lost on me. I want my story to run from the protagonist being a child at school (when the idea that the world is not such a good place seeps in) to the moment he finally resolves his story when I estimate he would be in his late 20s. So specifically: How do I go about stretching out these interesting parts and filling in the gaps between them without being boring or boring myself?
Read more novels. See how the great writers do it, and learn from them. Remember that short stories and novels are different. A novel isn't just a longer short story. There are often times more characters and more subplots in a novel. Reading and studying novels is the best way to see the difference for yourself.
First don't think of them as boring parts or filler. Everything is story, everything is integral. Never treat any part of your novel as if you're hurrying to get to the good stuff or the reader will feel it. Keep those details that are in between the big scenes interesting - that's how you stay focused and interested. Take a peek at Charlie and the Chocolate Factory. Before they get to the actual scenes in which the next kid will be offed - there is some funny banter and the square candles that look round and the pink candy boat streaming down the tunnel. Dahl keeps it interesting.
A good first step would be to pick any novel that you've read before and know you liked. Go back and re-read it, not as entertainment, but as a tutorial. Makes notes as to how the author presented his/her story. Did (s)he present multiple points of view? How did scene changes differ from chapter changes? How did (s)he foreshadow events? How much description was there, and at what points? What techniques were used to control pacing? Then, pick another novel that differs greatly in style or subject matter and do the same thing. Compare one to the other. How does your conception of writing compare with what you see successful authors do? One immediate thought - having your story run from childhood to adulthood suggests backstory. Only include as much history as the reader needs to understand the story (something else to look out for in your comparative reading). Best of luck.
You might not. You may write thirty thousand words for a single day, and another twenty thousand for another day ten years later, and so on. The story doesn't need to be spread evenly across the fictional time in which it occurs. I realize that doesn't actually solve your problem, but if you're going down the path of peppering the intervening years with events just to increase your word count, I wanted to suggest that that might not be the right path.
@thirdwind and @peachalulu have it right. Short stories are not just stories that are short, and novels are not just stories that are long. They both have very different purposes and very different techniques involved. While short stories are often snapshots or scenes, novels are not just a series of scenes with filler in between. There's a flow involved. Novels need to be deeper--they need multi-layered character motivations, goals which don't always align, opposing forces to set them back, additional characters with their own agendas, other goings-on that either directly or indirectly affect what's happening--there's not enough space in a short story for that kind of complexity, and simply taping a bunch of "interesting parts" together without looking at it from a structural standpoint will show a lack of that essential complexity. Character arcs don't just take a break at the interesting parts. Every part should be an interesting part, and that's not meant to be a generic platitude.
Thirdwind is right on target with this. The structure and pacing of a short story is different than a novel. To see the structure, with pen and paper or index cards, keep track of the plotlines, how they twist and advance, transitions used, instances of character development and so much more. Sometimes putting it in an outline or paper form, boiled down, the structure is easier to see, and you can apply that structure for the novel you intend to write. I will say that when I am coming up with a plot for a 'story', I spend time examining if it's enough for a short story, or is big and complex enough for a novel.
Thank you for all your replies I think the lack of multiple sub-plots might be something that's setting me back. I have one major sub-plot that ties in to the main plot in a big way, but I think it's coming up with more of them that are still worthy of a place in the story that I'm finding challenging. I will, however, take Thirdwind's advice and study some of my favourite books more.
Well darn, everybody beat me to it. All the advice above is good advice. I'll be short. Just keep in mind that short stories often have a tight focus, i.e., 1 or 2 big ideas, a small cast of important characters, a short timeline, and one major central event. A novel is much more expansive, not only in length. It will usually have a central plot complemented by subplots, a wide cast of characters who can come and go throughout the story, multiple ideas that may drive different sections, and so on. Short stories and novels also utilize "scene" a bit differently. You'll want to read more novels to pick up on how novelists use language, dialogue, exposition, scene and sequel, chapter and so on to control the pace and flow. You might want to invest time in plot and scene maps, and fleshing out what you want to do with the story. Don't think of anything that isn't a major plot point as filler or extra.