How I do it (III): The designer phase
Once I have a more or less consistent scheme, the next step is to develop each part of it. For this, what helps is to group the whole schema into chapters.
Each of the chapters also has to comply with the schema start, development, and conclusion, which can be further simplified. I describe in a few lines what is going to happen in that chapter, the starting point and the end point.
The great advantage of this approach is that the blockages are minimized, you have already defined where you want to go. All you have to do is to find a coherent way to get there. In my case, this is when I write most freely. On more than one occasion I've had the feeling that the plot develops by itself, that's just a consequence of good planning beforehand.
And I have to say, it is one of the best sensations I have ever experienced as a writer.