I'm having a great time writing this thing that I can't get too specific about, but I'm severely blocked on today's work, so I thought I'd talk about writing instead of writing, in the hopes that it shakes up my brain and lets me get back to writing.
When I write fiction, the first thing I do is break the story into acts, then into important things within those acts, and then into a few key scenes. Think of it like a map, with some pins pushed into it showing a route from beginning to end. It's a zoomable map, so some of the pins are closer together on a well-defined path, while others are more general.
Once I have that done, all I have to do is connect those pins into a narrative, allowing myself the freedom to wander off the main road from time to time if something catches my interest*. I need to be able to visualize scenes as I write them, and I need to hear the characters speak in their own voices, so they don't all sound like me. On the first draft, though, I don't worry about all that too much, because I know I'm going to get another shot at it before I turn it in, and it is always easier to rewrite something than it is to fill up an empty page.
I usually find some really interesting side trips during the first draft, either because a character told me to go left when I had planned to go right, or because a scene felt false, for some reason. I love that, because when it happens, I get to watch a little story unfold in my head, like I'm watching a movie, because I didn't plan for it to happen. The evil twin that comes with that, though, is that there are occasionally things that I thought were awesome, that I couldn't wait to show readers, but discovered that the story didn't need them.
So, hear me now: Sometimes, you're going to have an awesome idea that just doesn't fit into the story, and you have to let it go. It's still awesome, and you should keep it in a file for something else, but you could make yourself crazy trying to force it into a scene that clearly doesn't need it.
As evidence, I offer the last six hours of my life, and now I desperately hope my goddamn brain will let me get on with the story, because I haven't accomplished anything close to what I needed to accomplish today.
*I figure that if it's interesting enough to catch my interest, when I already know what the whole thing is about, it's probably interesting enough to catch a reader's interest, so it's worth exploring.