It takes a lot of practice not to edit while writing. New writers and those returning after hiatus often complain that their writing is “bad” while half-way through the first page. The urge to pick and poke at the words leads to great procrastination, and worse, it leads to a belief in self-criticism.
One exercise I find helpful in leaving this habit behind is the “stream of consciousness”, a non-stop flow of words written for a pre-determined time (usually fifteen minutes for me). This gets me in the habit of not checking my work as I go. It is difficult at first because we have an internal censor telling us, “Oh, but you can’t write THAT!”
The censor can go copulate itself with a rusty iron poker. It is a liar and should be beaten. The censor cheats us of ideas, denying us the irrational discourse which makes a story thrive. Even worse than telling us what we can‘t write, it has the audacity to tell us what we CAN, and that is unacceptable.
Back to the stream: let the words flow. Any words, it doesn’t matter; they don’t even have to make sense. You are intentionally writing one word after another without checking to see if the idea is good or bad. Fifteen minutes, once a week, every week, and letting the words flow will become second nature. Hell, two minutes is fine if that’s all you have. The same is true of all writing. You can edit only what exists, and it won’t until you put it on the page.
Now, get busy.