I often start the year with a descriptive writing focus, it gives me a chance to see where my students are in their writing, its engaging but most of all it teaches them writing devices and how to engage the reader early in the year which makes teaching writing all year more exciting and their writing way more interesting.
I find one of my favourite ways to introduce this is through the story of The Twits by Roald Dahl. He does such a fantastic job of painting a picture of two absolutely foul individuals and the kids find it hilarious. Its also a quick and very engaging read for you to get your read aloud's started.
My first writing task, (usually about half way to 3/4 of the way through the book) I have the students write a character description of Mr. Twit. I use it as my diagnostic and create my writing lessons around what my students need. I also have them use their ideas to help me create an exemplar of a character description.
Then when we are completely finished I have them write a character description of Mrs. Twit and use the same success criteria to assess their writing.