Whether you've written a few novels, or have yet to complete your first, you likely have a slush pile of unfinished, barely started or merely outlined story ideas. I propose that these incomplete thoughts are worthy of further consideration, and if not in the form you originally proposed them to yourself, than perhaps as a piece of flash fiction or a short story?
If you're anything like me, you have scenes and dialogues - that in a moment of inspiration - you had to jot down. Sometimes these moments turn into minutes or even hours. You may not be working on a story that will be suitable for this flash of genius, but if the scene has a beginning, middle and ending, or can be expanded upon, you might just have yourself a tidy little short, or work of flash fiction.
I have been surfing through my own pile of start-ups and see merit in each of them. Some are honestly a paragraph - a witty piece of banter between two people - where others are stories which developed on their own with no clear end in site. Revisiting them, I have managed to find an end in some, expanding on others to complete a piece of flash fiction, or simply edited a short story I had written years before.
My point is that these stories caught in moments of inspiration weren't for nothing. Inspiration brings life to any thought, and when we write that thought down it becomes a story. So why wait for the right novel to include your unique dialogue and character piece? Do something with them now!
I'm currently working on a number of stories from my slush pile; even one which features characters from my trilogy. A look at life for those I didn't kill off. Just 4-5,000 words. But enough to tickle anyone's interest who'd read the trilogy and wondered about a fourth book.
This practice can also be helpful in moments of writer's block. Revisit a train of thought you never completed. You know you have them in that folder marked 'Unfinished' on your desktop. People love a story they can finish quickly on a trip into work or and afternoon in the sun. A compilation of these stories just makes sense.