How do I improve my comprehension skills for the listening part of the exam?

In order to improve your comprehension skills you need to - unsurprisingly - practice. The key to identifying the right vocabulary and answering correctly is tuning in to the speed and cadence of spoken German. While there is a lot to be said for listening to German radio and music, a lot of the time this is done passively. To really see an improvement to you comprehension skills you need to engage in active listening.
So how do you actively listen? The key is staying focussed on the task and working with the audio. Pick a German film that you love, or choose one that you are studying and watch it once with English subtitles to make sure you have understood everything. Then, watch it with German subtitles, pausing and replaying sections as you go to ensure that you can see - and hear - exactly what has been said, matching the voices to the written words. As you go, make a note of all the new vocabulary you have encountered. You can start practicing with short audio bites and videos with both German and English subtitles. A great resource for this is the ‘Easy German’ Youtube channel. Eventually, you can start to tackle past examination questions alongside tapescripts. Using marking schemes will give you a sense of achievement as you improve. As tedious as this repetitive technique may sound, if you stick with it, you will build a huge bank of vocabulary, do really well in the exam, and be able to watch films without the subtitles!