Outline. Outline. Outline. If you have a detailed outline there is nothing to get you stuck. If you need, more ideas there are many great ways of generating ideas you can try. If you are having character problems, flesh out those character invent side stories in their background, that can be added to the story your working on.
Find a Muse.
write what you know
Try a new career
take a break get out and observe the world aroung u and u will find something to write about very quickly there are at least a billion stories out there
Get away from it for a while. Read a book, watch a movie, go for a hike.
Writing isn't just about putting words on the page. I'm not a person who writes every day. I'm not that disciplined. But when I do, I write a lot. I call it the volcano (or barf) mode. So don't feel that you're blocked because words aren't making onto the keyboard. If your story is percolating in your head, then it's part of the writing process. <br />
If you're really blocked, don't have ideas about what to write, (I've never had this problem, sorry), I've heard that walking or just doing something different than your usual can open up new ideas for you to investigate.
get a jar of glue. pour it on your seat.
Take a walk, write about what you see and what you feel