I'd like to add my support for the outline idea. I have an alarming tendency to write really long stories. My current project has been in process for two years. It's over 600000 words (that's about a 2600 page novel, for reference), and I still have 1/3 of the story left to write.
Before I start writing a story, I like to outline the whole thing. I decide what I want the story to be about and exactly how I want it to end, and then I decide on a first scene. After the first scene, I keep adding scene descriptions until I've made my way back to the last scene.
The outline doesn't have to be a perfectly written outline. You can always change it. You don't even have to use it in the end. But it really helps to have at least one road to the end mapped out. I find myself wandering off into what-if? detours and new ideas all the time, but when that happens, I always pause to retool my outline and make sure I can still connect where I am to where I'm going before proceeding. In fact, my current story is on outline version 8
I used to have repeated trouble with starting stories and not being able to figure out how to end them. It's easy to get overwhelmed, and it feels terrible when you've spent so many hours on something, only to realize you have no idea what the hell to do with what you have, which only compounds the anxiety of trying to figure out how to proceed. Since I started outlining in full prior to beginning my first draft, I haven't run into that problem again.
My other recommendation is, even if you're stuck, force yourself to write for at least an hour an evening until you get unstuck. It doesn't matter what you write, just write, even if it's gobbledygook. You want a scene with Lois & Clark? Try stream-of-conscious dialog without stopping to think about it too much. See what pops out of your brain. I find a lot of times, the mere act of sitting down and typing the first paragraph is all I need to get out of the grips of writer's block inertia.
For instance, start with,
"Clark," Lois said, "What the hell are you doing?"
Well, what does Clark have to say to that?
Set your timer for 60 minutes, and tell me
