You've been slaving over your giant epic novel for months or years, and then you get to a point where you don't know what's next.
The diehard outliners out there will probably shout from the hilltops: "That's why you need to outline!" However, my friend, even outliners can have this problem, because they can get to a point in their story where they simply don't know what's going to happen next.
To remedy this, you can do one of two things:
First, start something new. It could be you're just thinking about a new idea, a short story or a new novel. I believe it was Chuck Wendig who said (paraphrasing!) to keep working on your current project until it's done. Great advice, for sure. But if it's gnawing at your mind, take an hour or so and write the darn thing.
Also, it could be that your story needs a little spice. I'm not talking a sex scene or blatant erotica. I'm talking a change of pace. On my first novel--a deer hunting horror story I wrote back in college--I hit a rough patch near the beginning, when the four characters were going out into the woods, because I didn't want the story to be a "Guide to Deer Hunting Techniques." I then had a vision of a boy, out for a bike ride one final time before winter, getting into a fatal accident and all of the events leading up to that one moment. Bingo! I wrote the scene as I envisioned, which jarred the story in a slightly different direction. Looking back on it now, I don't know if I'll ever keep it in but it did change the pace.
I have written stories where I change point-of-view for a chapter here and there, just to change things up.
Second, if you can't think of something, walk away from your computer or typewriter and think. Brainstorm. Force yourself to come up with twenty different ideas. Don't go with your first or even your second, no matter how well you think it is. Come up with twenty ideas.
What have you done when you've hit a rough patch in your writing? Please comment on it.