Writing to define one's own learning. At the beginning of a topic or a class, ask students to write to remember, select, and record what they feel was their most important learning about a given subject the day before. By focusing attention on previous learning, this kind of writing prepares students for what is coming next. Writing to summarize. Writing to apply.
Students can write to speculate about the practical value of their learning.
From such writing, and the discussion it generates, you might discover new reasons for what you're teaching. Writing to inquire. Students will not likely develop the habit of inquiry unless they are urged to ask questions. Stopping at odd times and asking them to write a question elicits many useful responses. The questions might bring out what the students don't understand what they would like to know more about some speculation about a relationship between what they are working on now and something they have done in the past a need to have the purpose of the current subject or activity clarified.