Hey all,
Unfortunately, I'm not very familiar with 12 Angry Men. It is fairly new on the syllabus and from what I've heard is not too challenging.
For the text you choose at the end of the year, ideally, you have a choice between two texts if you know both quite well. However, most students tend to concentrate on one text a bit more. Whatever the case, answer the prompt you are most familiar with. Practice does produce consistency. It is important to choose a prompt that you feel you have, at least to some extent, explored before.
You should practice writing full essays / exam papers when you feel that you a solid grasp of what is expected in each essay type. Sure it doesn't hurt to keep practising full essays from day 1, but you can get the same level of feedback by writing paragraphs. I would suggest being able to pump out solid full essays by the time term 4 comes around.
The Quiet American is one of those great texts in English where average students will have a substantial amount to write about, and exceptional students can really show off on. Therefore, I agree that it can be both simple and complex, depending on the level of comprehension a student is aiming towards. I love the text.
All the best

Yang