Do not write more than six paragraphs per day. That is, do not write for more than three hours each day.
This rule should govern not just your practice but your planning. The point is not simply that you shouldn’t write for more than three hours a day. Since you should not write when you haven’t planned to, you should also not plan to write more than three hours a day. I recommend planning between one and six 27-minute writing moments in a continuous series, separated by three-minute breaks.
It is very rare that the seventh paragraph will be satisfying to write. It also usually difficult to think of more than six discrete truths to write about the day before. This is not a physical limit on what you can do in a day. Most of us have the experience of writing five or six or more hours and producing 2000 words or more in a day. This rule is restricting you to work in an orderly, comfortable manner. Working in this way will have positive effects on your style. And it will also be more enjoyable than trying to power through a whole a day of writing. If you start at 8:00 or 9:00 you can be done comfortably before lunch. Relax, enjoy the success, and get on with the other things in your day that need doing.
People rarely think of the cost of writing. When you are writing you are spending time that could be spent doing something else. For the first three hours, you can be pretty sure that it’s a good investment. The prose you are producing will, with reasonable certainty, make a contribution to reaching your overall writing goals. After that, you are probably producing prose that you’re likely to discard or completely rework.
More importantly, after three hours of writing, the act of writing itself is not making your prose stronger. It’s not improving your style. On the contrary, it is during this time that you are getting worn out and building your animosity to the craft of writing. This is when writing becomes a chore, even if you feel like you’re “in a flow”. It’s often an illusion and you’ll regret falling for it later. Don’t push yourself beyond the limit where writing is both enjoyable and deliberate. Don’t do so much that you lose track of what you are actually doing. Don’t get caught up in it.
Hemingway used to advise writers to stop when they “had some juice left”. He meant that they should stop at a point where they know how the story would continue, not when they had run completely out of ideas. That way it’s easy to start up again the next day. My tenth rule is also intended to conserve your “juice”, albeit in a slightly different sense. Don’t use yourself up in one day so that you can’t work at all then next. Working an extra hour today can cost you the ability to work several hours the next day.
Finally, like the 200 word limit per paragraph, remember that 6 paragraphs per day is also maximum. There is absolutely no shame in writing “only” two, three or four paragraphs on most days. Slow and steady wins the race. Don’t try to get anything done in a whole day of writing. Teach yourself to make use of half days for writing. You won’t regret having that ability.