Last week I wrote about 'using what you know'. Here are some more quick examples of how you can make a 'difficult' question much easier:
1) Describe something that you collect.
Most students panic because they don't collect anything. But this question is easier than you think. If your hobby is listening to music or reading books, just tell the examiner that you collect CDs or novels. You could talk about your "collection" of clothes or shoes. Everyone has a collection of something, even if you don't call yourself a collector.
2) Describe an important decision that you made.
Easy. Just talk about the subject you chose to study or the career you decided to pursue. If you moved to live/study in a different country, you could talk about that.
3) Describe an important letter you received.
Use the answer you gave for number 2 (with a few small changes). Talk about the letter you received confirming your place on a university course, or confirming a successful job application.