In my wanderings around classrooms I have seen a lot of teachers working with students on developing descriptive writing and expanding sentences.
I find Telescopic text the best way to show students how to expand their writing. I demonstrated to a class the other day by showing them the 'I made tea.' first.
Next I showed them the Telescopic Text Write site. We typed in one of the simple sentences their teacher wanted them to expand around their poem 'My mother saw a Dancing Bear.'
I have tried this several times with students from many different schools and it has always been very successful. Their general writing improves because they become aware of how to make sentences more interesting.