Definitely watch the 1957 movie, it helps you understand the entire play a bit better and actually help you view the entire play from how Rose wants the audience to see it. For example, the opressive feel of the room can be picked up from the movie whereas you'll most likely miss that from reading the play itself. Also, there are many symbolisms that you can spot throughout the whole movie. I suggest you read the play, watch the movie and finally read the play WHILE watching the movie. Of course, read it multiple times throughout the year/before the exam too.
It was the first year of studying this text for us last year so there weren't many prompts we could write our essays from but by the nature of the play, I don't think the prompts can vary too much from each other. I'm sure you could already guess a few of the 'standard' prompts out there after reading it so you're able to develop some solid ideas and modify them in accordance to different prompts. That's what I did for the SAC and practice essays because I wasn't given much to begin with and the limitation is what lead me to do another text for the exam not 12 Angry Men. Also, keep in mind that while the play seems fairly straightforward, there are different layers into it - it's not just about the law, the jury, democracy, etc so stick to your ideas consistently to let your understanding show through writing.