1. Take a break: if I have been writing pages and pages and suddenly I don't know where the story needs to go, getting away from it helps my subconscious to start putting pieces together. I read a book, a blog, or just get out of the house. This only works when I’ve already put in the work though. Taking a break after ten words is a cop out, which brings me to…
2. Summarize: Sometime the scene isn't working yet. I have been known in first drafts to write; "they fight, add it later" and move on. On the same note imagine the scene is already written. You will be surprised what details you find that already know about that scene by writing the scene right after your troublesome one.
3. Calculate: As soon as I know what type of book I am writing I have an idea of the length it needs to be. Young adult is about 50-100K. Most novels are around 80-100K of words with fantasy going as high as 150K (or if you are Jordan or Rothfuss MUCH higher). I pick a number in the range and use that as my goal. Then I figure out chapter length, 2-5K for me, and figure out how many chapters I need, I rounding up. I have a spreadsheet with words, pages and chapters to go to meet my goal and a count for how many more words to go in a chapter. I like the organization and tangible measure of progress. Why yes I have an inner type A.
4. Outline: Once I have that first rush of story that tells me who and what I am writing about, I try and figure out what needs to happen to get my characters to the ending. If I get stuck in the outline I write a ending and work backwards to figure out how to get there. I write about 10-400 words per chapter. Sometimes I write out major bits of dialog and description, other times I write, “Tie up the fight. Be clever! No pressure here.”
5. Don't go backwards: As you are writing the story you will get ideas for the parts you have already written. That is great, but if you break off writing and scroll back to chapter 3 and find the scene that all of a sudden needs to have ice-cream in it to emphasize the deep spiritual meaning of waffle cones in chapter ten, then getting back to where you started is much, much harder. I've heard of writers that keep a notebook next to their computer and jot notes down as they come up. I type red text into Word right in the middle of what I was doing. I fix it during the revision phase. I don't look up names or facts either unless it's vital. If I don't remember what I named Matt's little brother then I type "xxlittlebrother" and keep going. The xx makes it easier to search with Find and Replace later. I also change my text to be minuscule on the chapters I am not working with so I can't get sucked into the story or into doing fussy edits yet.
6. Type something: If I absolutely can not figure out what comes next then I start free typing. Delete is always an option but usually something will come out a few words after typing "I don't know what to write" or “What do I need to happen next?” I find the physical part of typing to be relaxing, I’ve never been what you would call normal.
7. Work on something else: I work on a couple of projects at once. Writing something fun and with out the pressure of being the "first draft of X project I am going to submit professionally" helps me get words. And perhaps that space squid story will get sold someday.
8. Be bad: I give myself permission to be horrible when I first draft. I overuse words, use trite metaphors and ignore the spelling check. That is what the second draft is for (and the third and fourth and…) On the first draft I need to get the ideas down, meet my characters and write an interesting story. I think of it as the pencil sketch for a painting. Once it’s down I can erase like crazy, fill in where needed and edit, edit, edit.
9. Research: Sometime knowing the whys about your environment can give you new ideas on how your character would act. Just don't research more then you write. It's easy to fall into the trap of researching every single detail. Research is great, the story is more important.
10. Read it out loud: If it's not working I go back to the last place that the writing did work and read out loud till it doesn’t. I can usually hear where the narrative is off and how to fix it.