A simple guide to show how to prepare teaching materials
https://www.cieej.or.jp/toefl/mailmagazine/mm43/SELHi_appendix1.pdf
How to create teaching materials
http://www.bmj.com/content/326/7395/921.1
Picking and Choosing Digital Content
http://www.edweek.org/dd/articles/2012/02/08/02digital.h05.html
11 qualities of good digital content