I guess I'm lucky or hard-wired somehow, but I've never had trouble writing. When it's time to write, I sit down and the words come.
There are times when I get stuck midstream, but I have found that if I just write something, anything almost, and just keep writing, sooner or later the words get around to the project I intend them for. I wrote a shopping list once and, little by little, project-relevant stuff came forth and away I went.
For some reason, I am able to avoid self-judgment as I write - that may have something to do with it. I write and worry about fixing it some other time...or deleting it altogether.
When I stop for the day, say, I always take care to stop at the place easiest to finish. Writing to a good stopping place is death; I will never be able to pick it up the next time I sit down. Rather, I force myself to stop at the point where I want most to continue on, at the point where I know exactly what I will write next, whether it's a word or sentence. Mid-sentence is best. If I think I will need a little reminder the next time I sit down to it, I space bar a few spaces and enter a key word that will remind me my train of thought and tone/mood.
But, mostly I feel lucky and just try not to abuse the privilege.