I found this article by David Cutler about the importance of modelling high quality writing for students in more than just a five minute window on the the whiteboard. It needs to become a meaningful process every time we pick up a pen and engage with students.
This is definitely something I have been guilty of not doing as well as I could when I looked at his six focal points of how teachers should writing effectively.
1 - Teachers need to be effective writers
2 - Teachers need to share their writing
3 - Teachers need to write for their students
4- Teachers need to run writer's workshops
5 - Teachers need to seek feedback.
6- Teachers need to write about the real world.
It is a great article for anyone teaching writing and is available here.