I like to unpack the writing rubric with students and have them engage in conversations about their writing, based on the language of the rubric. I have also started to audio record some of the younger students' reflections on the iPads. Older writers would be able to do this independently.
I, too, ask my students to write notes to me (and to each other, when they are peer editing) on their written work. It is wildly helpful in focusing my own comments back to them. Here is a link to the list of protocols they use when writing their notes to me: https://docs.google.com/document/d/1rmNl5aykbO4398qrBoooEj4A0pe9ytLuszdHo7eHQ5Y/edit?usp=sharing
Woops. That link didn't turn up live -- I'll drop a copy in our shared folder!
Using the Comments feature in Word or Google Docs, or other writing tools, would be an interesting way to encourage students to annotate their own work. Ask them to explain why they used a particular quotation, or even reflect on parts they cut out or added.
I've had students create mind-map-type visual representations of their writing process, which I like in theory but I'm still tinkering with in practice. I like the idea of having students map the development of their writing and reflect on where they started, where they ended up, and how they got there, but students need a lot of support and scaffolding to be able to do this sort of thinking.