Novel =/= Short story

So, I've been writing since I was very young.  The problem has never been, "What to write about next" - but more along the lines of keeping up with the last thing I wrote about. 

As in, all I ever seem to get are half stories (the longest being about 20 pages). Any tips for actually writing something substantially longer,  instead of ending up with a short story?

Plan it out first. When you know where the end is and where the landmarks in your plot are, it will be so much easier to fill in the blanks. Once you find the scale of the piece, the events that fill it change from being important story elements that motivate the plot to being one more thing in the book. And since you know the shape of the book, you know what sort of thing will fit and you can just put it there. The plot is there and will happen on its own, see, so you don't have to worry about advancing it. You just fill in the gaps with expository anecdotes that explain motivation, fascinate the reader, and so on. And you describe the plot events in detail, of course. But everything comes from knowing the scale.

DISCLAIMER: I write music, not prose. But my gut tells me this will be helpful to a wordsmith as well. There are probably some (many) writers who can begin at the beginning and wander their way to the end. Since you are not yet one of them, it would behoove you to attempt premeditated structural techniques.

You have been writing short stories for quite some time? Want to tell a longer story? Use the short story sequence format, where your short finished pieces follow the plot, but not the form (as in, the story is continuous, but composition is every time a new thing with each piece having it's own beginning and end, unlike that of the chapters in the novel, which aren't compositions on themselves, but parts of a composition).

Now, if you really want to write something "long", you should consider that it takes accordingly more material to keep things substancial. Just writing longer about stuff isn't going to do, or you'll end with just another shitty novel, of which we already have too many.

The difference betwen a novel and a short story is that the short story is more of a picture or a short cause-result sequence. Now, the novel consists of several different happenings which, _related to one another_, constitute an aesthetically pleasing combination. The is: the novel should ALWAYS be more than sum of it's parts. You may be writing about however small things, but together they should form a really grand (aesthetically, emotionally or other) picture in your readers imagination. Sure, some writers just write overly long stuff simply because novel is an established format: that be mediocre and bad writers. Good ones, on the other hand, write the shortest they could, and if they write a novel, then it must be the shortest they could to express a poetic image convincingly and without preaching like a faggot.

So, simply put:
- got a long story? Use a sequence of finished short stories to tell it.
- got a complex idea? Are you sure you aren't just going to waste your time on somehting you aren't all that interested in? For this your "complex idea" being the most interesting stuff in the world for _you_ is a must and an absolute prerequisite. Yes? Fine, then: start composing, with this in mind:
1. The purpose of your whole book is expressing this one artistic idea; everything else is disposable.
2. Composition is your instrument for driving _it_ out just as you have it in your mind. Every scene should be moving you _there_. Every major character should be there to imprint upon the reader the bigger picture; don't forget the next point, though:
3. The only elements allowed to be slightly outside your main goal are things that make your story more convincing. Character development, for example: so that you wouldn't have cardboard cutouts that could harm your big picture with their ugly presence, you know. Some dramatic or awe-inspiring happenings, too: so that you could pre-inspire you reader and feed him some awesome before you hook him, perhaps.

The two major differences between novels and short stories are description and pacing. A short story will be written generally in the style of Neil Gaiman or Phillip K. Dick; you'll get a person doing this, then that, then this, then maybe his inner thoughts, and then he'll do this. All you need to know, rat a tat tat. A novel, on the other hand, a big novel will have pages dedicated to the background, the characters in a room who don't say anything, the background noises, the history of that table over there. Some, of course, won't have any need to do things like this. But even short novels, say something like Max Barry's work, take the time to lay out a world that these people exist in and introduce you to it.

Good ones, on the other hand, write the shortest they could, and if they write a novel, then it must be the shortest they could to express a poetic image convincingly and without preaching like a faggot.
>>2 here
That's what I mean by scale, BTW.

>>5
>>3 here,
basically, my whole post says the same thing as your >>2 , as I can see now.

>>6
Oh, I don't think so. At worst, you wrote out my subtext (and vice versa).