All I write is short stories. I've done it as a kid. I like having an idea and then being able to vomit out the whole story onto a page in a few hours. Even if I take breaks, and take a couple of days, I still feel like I am rushing to the conclusion.
Granted, I've only tried to write a novel a few times. Those times I tried, I couldn't seem to break out. I say break out because I feel trapped. I'm trapped by my tendency to lower the scope of the story while I am writing. Or perhaps the story I had in mind had no room for large scope at all. My main influence is HP Lovecraft; I'm sure this doesn't help.
My concepts go something like this: People in a small town are leaving because of this disgusting, ancient, broken-down mansion that is stinking up the whole town. The authorities send a couple of cops to scope out the inside of the mansion because some children go missing and they might've went inside. The cops go in, and it's very gross. There's some half-dead residents inside. There's someone mysterious in the basement (some diseased freak chained to a wall).
Then I started writing, and, lo and behold, I got another short story on my hands! I'm not done with this story yet, I just struggle fleshing it out; I don't see how I can turn a two or three page story into a 400 page story. I'll admit I don't know how to write characters, first off. Usually it doesn't matter because the point of my stories is not the characters, it's the setting. The setting is much more important in my eyes and is the main focus of the story, which you can get away with in a short story, but likely not in a novel. It's shifting focus from a setting driven "plot" to a character driven plot that I think is causing me issues. I mean, how do I go from "this house is gross and scary" to "He who controls the spice controls the universe (Dune reference)." I don't necessarily want to write a sci-fi espionage political thriller either, I like the themes and genre I'm writing with now.
What are your tips on how to break free from tendencies towards writing (very) short stories when trying to write novels?
As far as my own ideas, I'm considering trying to rewrite The Lord of the Rings from memory (in my own words) and seeing how many pages I get. That sounds like a cool exercise. Even if I only get 10 pages, that's still better than 3.
Also, the "diseased freak" I mentioned earlier that was in my story was meant to be the main character, but I didn't know how to write a novel where the main character is some freak chained to a wall.