"there is no specific practice for diffuse thinking---one can say that it comes naturally. The only requirement is that we do focussed mode tasks and then take breaks in between.
As taught in this course, taking a shower, going for a walk or a bicycle ride, singing a well-known song, any form of physical exercise, and even taking a nap can cause our brain to work in the diffuse mode. Even indulging in semi-mechanical tasks like household chores or driving may help. But the main point is that, focussed mode of thinking should precede such diffused mode activities, for it to be helpful.
diffuse mode thinking is when we are not seriously thinking about the problem, and are instead doing other activities like walking, exercise or sleeping. So, diffuse mode first (with no focussed mode at all) can not be useful. A focussed mode first, even if a very short one, is very essential before the diffuse mode."