In preparation for tomorrow’s lesson, you could do worse than familiarise yourselves with the BBFC website. In particular, you should check out the guidance for the following ratings: U, PG, 12 and 12A and 15.
There is also an excellent Education section which has loads of useful resources and information, including an opportunity for you to ‘Rate a Trailer‘… which is an exercise that will provide immense use to you as you finish your own! (Hint! Hint!)