Explain to him/her why it’s important to work together. Many times teachers will grade based on teamwork so if he continues to be stubborn he will cost the whole group. Try explaining what your strengths are and dividing the work based on that. That way everyone can do their share to the best of their ability
Either the 2nd or 3rd bullit point
A short story conserves characters and scenes, typically by focusing on just one conflict, and drives towards a sudden, unexpected revelation. Go easy on the exposition and the backstory, your reader doesn't need to know everything that you know about your characters.