Never write a paragraph that you have not planned the day before. Never write at a time you did not plan to.
I know this is hard. During the period of discipline — that is, during the eight weeks you have decided to write very deliberate prose in an attempt become a better writer — try as best as you can not to write spontaneously. Don’t write when “the mood strikes” or you are “hit by inspiration”. Part of the discipline is to train your muse not to show up at the most inconvenient times. The way you do this is to make a quick note of the idea, and then to resolve to write about it at your earliest possible convenience.
This doesn’t necessarily mean you have to wait until next week in accordance with Rule #2. After all, while the idea to write about something may suddenly hit you, it may be something you have known for years. In that case, all you have to do is wait until tomorrow to write the corresponding paragraph or paragraphs. Just let the creative side of you know that the writer needs a bit of warning before the work can be carried out. You need to give your unconscious time to catch up. In order for this unconscious process to work properly, without anxiety, it must count on you to do the work you plan at the time you planned to do it. This also means not changing your mind in the middle of paragraph and writing something else that just occurred to you. Stick to the paragraph you planned.
Stephen King rightly said that “your muse has to know where to find you”. But s/he also has to stop calling you at work. And s/he will stop doing that when s/he can count on you to show up at the planned writing moments.
The other side of the bargain is that you can’t just summon your muse at all times of day and night whenever you feel like it. Sometimes what you thought was the song of angels was actually just a vague hunch. Once you start writing, you realize the idea wasn’t as good as it felt. For the eight weeks of the Challenge, I’m asking you simply not to have this problem. Don’t act on this feeling. Write according to your plan. I’m suggesting that you resolve to write only at the times you planned to do so. There will be no ambiguity about whether you are following this rule.