The Trick to Writing
Having been at this for a few years now, I've learned some things about how to overcome the most common barriers to writing. When people approach me and ask how I became so prolific when they struggle to even get started, the following is what I tell them. I'm sharing it here so that it can benefit more people.
The first problem people come to me with is the "blank page" problem. Being faced with a blank page and either not knowing what to write or, more precisely, worrying that whatever you write will be "wrong". You've got this amazing, fantastic story locked up in your mind, and you worry that you won't be able to do it justice.
There is no exactly correct sequence of words you need to write. Banish that notion from your mind at once. Do you think movies are shot all in one take? Of course not. Loads of footage is never even used, left on the cutting room floor. But editing cannot begin until there's footage to work with.
Likewise, do sculptors produce marble statues out of thin air? Is sculpting an additive, or subtractive process? No sculpting can occur until there is a block of raw marble to work with.
The same principle applies to writing. The time to make it perfect is not while you're writing it, but afterwards, during editing! First you will need a body of text to edit though. Critically, you must realize that anything you write will technically be a book once there is enough of it. Don't believe me? Fifty Shades of Grey. Twilight. The Secret.
Okay, okay, not setting the bar very high. I know. That's not what to shoot for of course, but the basic principle of it is that you must write something before you can make that something perfect. It doesn't happen while you're writing it and never will. Let this realization persaude you to bulldoze ahead.
Don't try to write a perfect story, just describe the events you envision occurring in the course of the narrative. Then scoot back, read what you've written and realize that's a story right there. That's all writing is. Then, once every scene you wanted to include is in there and in the correct order you can begin to edit. Going over sentences which read awkwardly and "streamlining" them, reconsidering certain scenes, shuffling others around and so on.
This is the "make it perfect" stage, but there's no skipping straight to it. Something's got to get written first. So plow ahead, perhaps commit to writing a minimum of 100 words per night. If that's easy, add more until it isn't, like lifting weights. You may find your "fitness" as a writer increases over time as a result of this practice.
That's the biggest single "trick" I know of. There's a lot of little smaller methods I employ, some of which are worth including here. One is a dynamic outline; rather than have a predefined skeleton of a story, which I find constraining, I instead include at the bottom of the document a list of scenes and concepts I want to make sure wind up in the final version.
As I write each scene/express each concept, I delete it from the list. When there's no more list, time to edit. But not before then! Otherwise it's all too easy to fall into the trap of fawning over what you have finished so far, revising it over and over but not writing anything new.
This approach allows me to add in new scenes as they occur to me during writing without making a mess of some rigid schematic I decided on beforehand, and ensures that the completed story includes everything I wanted it to.
There's little worse than that nagging feeling that a story didn't live up to its potential, right? This is one good way to prevent that from happening. Integrating the various scenes and concepts is quite like the process of stitching together tifferent pieces of a quilt.
The last tool I want to mention here is the master idea document. This is where I store every good idea I have for a story. Most are not enough of a premise, on their own, to base a really compelling, worthwhile story around. But often there will be a few more "compatible" concepts I wrote down ages ago and forgot which I can see a way to combine into the same narrative. That way the story isn't a one trick pony, but a sort of constellation of related ideas which reinforce and enrich one another.
Probably if you've been writing for any length of time, some or all of these ideas have long since occurred to you. If not, it's my hope that what's written here is helpful.

Great post. One of the "ah-ha" moments I had early on was the realization that starting at the beginning is rarely the best way to start. In the movies they sit down at the old typewriter and tap out "Chapter One..." In real life you might start by writing all those favorite scenes that are in your head clawing their way out. Then as you said stitch them together. (kind of got cut off on that last sentence though...)