I only get "writer's block" when I have a specific plot problem involving a work in progress. If I don't know why a character did a certain thing, or can't determine a plausible reason for something to happen in my story, I can get gummed up and find it hard to write anything. Once in a while, I can work on a later portion of a book while I untangle the plot problem, but usually, the plot problem wins.
So I spend a lot of time thinking things over, getting inside the heads of various characters, trying to decide what they think they should do -- until I have unknotted the plot problem. Then I write.
I never sit down to write without some idea in my head of how the story is going to go, though. I have no shortage of ideas, no indecision as to what to write.