I never really run out of ideas. Usually I have heaps of them, more than I can ever get to. Usually I combine lots of my ideas for different novels and stories into one (usually this means I wind up with every teenage issue under the sun tucked into one 50k word novel, but I usually get rid of a few themes later, and it works out okay).
One thing that I do have trouble with, is when I'm in the middle of a novel. It's a bit like this right now. I know how the book is going to end. I've written the beginning. But this middle? What the hell am I going to put here? This is the point at which ideas & inspiration come in handy (especially if you don't like plotting your novels like me). Try these things:
- Record all ideas. You know how you'll be in the middle of a writing project and you'l have a genius idea that you aren't going to let yourself work on right now? Write it down. You'll forget otherwise. Fill up a notebook with ideas, inspiring quotes, random words and sentences. You might not se everything, but it will come in handy one day.
- Go out somewhere and just watch and listen. I like the library, or a cafe. Take notes. Don't just listen to conversation and watch people. Listen to the air conditioner going and feet scuffling. Listen to glasses chinking and the sound when the door opens. Write down what the ceiling looks like, and describe the dust in the windowpanes. Write it all down, or just absorb it all. Don't think, or think about everything. Just be amongst everything, without having a specific place to go or thing to do.
- Watch a movie or read a book. I get really inspired after seeing a great movie or reading a book I love for the first time.
- Take a break from writing. This can be very regenerative, especially if you write compulsively in intense bursts and forget to leave you house for days (honest, I don't do this. Much).
- Create a soundtrack for your work-in-progress. In the past, I've gotten ideas for character names and plot points from playlists. If you like listening to music while you write, a special playlist can be a good way to get into the writing zone.
- Make a poster/corkboard/scrapbook of visual inspiration. For an example, check out these posts I did for my current work-in-progress: 1, 2.