I wrote something about writing about something somebody else has written. I give the example of Eric Puschak who crafts video essays about other expert's work. Click through to read how to borrow the expertise of another to create compelling essays for an audience who may not be familiar with your chosen expert's work. Your writing improves merely through the process of taking more comprehensive work and abridging it; or work from another medium (say video) and crafting it as a blog post. It's sort of like writing a book review without the haughty critique.
Check it out here: The Secret Structure of a Compelling Blog Post