In my experience writing (at least writing fiction) consists of two different activities: the writing proper, in which you produce text, and the editing, in which you mostly get rid of text. Think of the editing phase as liberating the statue from the marble, and the writing phase as producing the marble.

These activities, since they are so different in nature, are best separated in time and space and tooling.

I produce in the early morning, sitting at my dining table in the living room, using a pen and paper. In the early morning your dreams still linger and your critical faculties are not yet fully awake. This makes it an ideal time for just producing stuff. I take this seriously in that I do not even allow myself to cross out words. Just keep on writing, and sort it out later. Later on the day I edit, sitting in my study and using a text processor.

As a side note, I would not recommend this practice for writing code.