I have two kinds of block, one where my mind is crammed with too much stuff and it grinds to a halt, the other is where it is completely blank. I think when I falter on a particular stretch of writing, I move to another section of the story and in some cases I have been known to start at the end and work backwards (haven't figured that one out yet!). When my mind is on overload, I find a visit to the swimming pool clears my head enough to get my creative juices going again. The biggest difficulty I have is getting started in the first place. Once I get going, I tend not to have too many blocks.