The Cambridge English Preliminary English Test (PET) relies heavily on students having a good comprehension of a wide range of language. Indeed, the first four parts of the exam are testing reading comprehension. From the official Cambridge website you can download the PET vocabulary list, and though while this is helpful it is in no way a conclusive list. In order to do well, you need to understand phrases and their synonyms. As in the listening exam, comprehension is evaluated on how well you are able to understand paraphrasing of key language and ideas and so it is important to build on your vocabulary by looking at synonyms as well as antonyms.
A good way to do help students do this that is to encourage them to record the synonyms and antonyms of key lexis you present, not as individual items but in sentences which show context. Activities like the one below can help students build their understanding in a more meaningful way than just direct translation.
Here is a synonym matching exercise on some key PET words and phrases that seem to come up time and time again in PET exams. Let me know what you think.