Just write. Even if it's crap just write.
This. Write what comes to you. Even if it's a sentence, even it's something unrelated. Just write it out.
I write little serials and short stories and one thing that really helps me, even if it sounds weird, is talking to myself. If I'm having trouble figuring out how a certain piece of dialogue is supposed to go. I talk out the conversation out loud to myself. Or if I'm having trouble setting up a set or details, I'll describe what's in my mind out loud.
Also another thing that I used to cringe at. Don't be married to your outline, and don't be afraid to scrap it and start from square one. If the ideas just aren't coming or it feels like it's a forced effort (besides just buckling down to write) don't stick with it. Cut your loses and move on. If it doesn't work, then it just doesn't work.