I don't write much, though I always tell myself I'll start again 'soon'. I find a few things that seem to work for me at least.
1) Try to fit in things into your writing that are personal. For instance, if, hypothetically speaking, a girl you were interested in told you that
she had no interest in you (this may or may not have happened to me this last weekend
) then that will provide a certain emotional slant to your
writing, and you might be able to find something that works.
2) Pay attention to your dreams at night. I don't know about other people, but sometimes I have some pretty cool ideas, and I'd try to write them
down so I'd remember them. For instance, I had one dream where I was watching this strange scene. Some guy had died and was about to be
reincarnated, but before he was, he woke up in a kind of 'between life' place with millions of sleeping/dead bodies and some mysterious character
that was running it all. I actually wrote the first chapter or two of that one, and I thought it was a pretty sweet idea, but eventually I got
distracted by other things.
3) Ask lots of 'what if' questions. For instance, 'what if' the president was assassinated? What would follow in the aftermath? What if aliens
made themselves known to the people of earth tomorrow? How would that change things? Or imagine strange scenarios and then try to fit a story around
it. For instance, imagine what would happen if a T-Rex started rampaging in downtown New York, or some crazy naked guy with a sword was running
around claiming he was King Arthur returned. Then try to find a story that would fit the scenario.
4) Sometimes you just get stuck on one story. If that happens, try working on a different project that day, and come back to the other one another
5) I've never tried this one, but it's one I've thought might work. Try writing some sort of fan fiction in somebody else's world. Write a Star
Trek story or something. (or whatever, that's just an example since the book I'm reading right now is a star trek novel and it came to mind) For
obvious reasons, that would probably not be one you could sell, unless it was in a shared universe like the Star Trek example. (JK Rowling might be
pissed off if you tried to sell a story about Hogwarts for instance :p)