When I have my classes write short stories, we begin with daily focused writing.
I give them a prompt with specific questions focusing on the plot diagram.
We made a class book which showcased their short stories, fiction, and non-fiction writing. I used this class to help students explore various aspects of writing and see which one they liked best.
I would say to start off the year, you should go over types of creative writing and make sure your students are familiar with those.
Write the story three times, each time from a different character's perspective.
Focus on the way the first person narrative can use language differently to define and distinguish characters. I am in the last term of 12th grade equivalent, and my writing wasnt that good until classes 9th-10th when I began to read seriously, lots of good stuff that had me enthralled and MADE ME KEEN ON WORDS AND THEIR POWER AND BEAUTY.
When should our admiration turn to worry, and when does it become a school's responsibility?
It is not easy to teach creative writing within the confinement of school.
At first they list features of it, describe it, spend time with the item holding it etc. After that they develop a story or poem about why the item is important or a time the item was present at an important time in their lives etc. A few ideas I have used successfully were to give students "beginnings" of stories, just a sentence or two to get them going and then ask them to complete the story and to have a story worked on serially, passing it around from one student to the next.
Another thing I like to do is bring in provocative pictures (a man dressed as santa driving a sailboat or a baby with two snakes in its crib etc) and having students create a story inspired by the photo. They seem to like this and it's a good way to break the ice for reluctant writers.