I’m not a big writer, but when I have to write a (fiction, usually) paper for a class, and get stuck, it always helps me to write a bit on my typewriter. Of course, this may be just me… 
Write every day for at least two hours. Never finish a scene just before you are finished writing for the day, that way you will not have a empty page in front of you next day. Plan to reward yourself with something you like after your two hours are up{ sounds childish but it works} If you can’t think of anything to write, start with" funny you should say that", she said. and start from there.
My advice is to just write what’s in your head, whatever’s in your head, even if it’s nothing at all. And don’t worry about writing things in sequence (as bjohn13 has already discussed). Even if you only use it as an exercise, if no one else ever reads it, you’ve written it and it does you good. I usually write for twenty minutes in the morning, when I first get up, and for as long as I can in the evening. Due to computer troubles, though, I’ve been writing in fifteen to twenty minutes slugs with long breaks in between. It’s been odd, but it’s worked okay, so don’t think “Now I have to sit down and write for an hour” if it’s torture. Break it up. Play with it. Write in the morning. Write at three a.m. Write at lunch. There is no formula.