When preparing for a test it is easy to get caught up in a test-only mentality, and that can mislead students into a false sense of security regarding their overall language skills. Regardless of whether the examinee is a second-language speaker of English, or even a native speaker, the fact of the matter is that a lot of the questions, and indeed entire sections of the test, are all to do with understanding and manipulating sentence structure. The only way to be able to do that effectively is by having a good working knowledge of and the right skills for your English grammar.
The traditional approach to grammar improvement involves learning, memorizing and reciting grammar rules until you are unable think about time without considering which verb tense to speak in. Of course this method has its benefits, and it is necessary to a certain degree – in order to gain an insight into the relationship between clauses, word types, voices and tenses, you simply must refresh your knowledge of the rules and ensure that you can identify complex, compound sentence structures. However, in order to really boost your grammar, you need to put in a lot of time practicing and applying the rules that you have learned, or else you risk just remaining stuck at the level of many learners of English – having a stellar knowledge of all the rules, and being able to quote them word for word in textbook fashion whenever questioned by a teacher, but possessing no ability to practically apply that knowledge by putting it into action in writing, or even by calling on it for textual analysis.
So what can be done to remedy your grammatical shortcomings? You need to up the frequency of usage of your grammar knowledge by not just memorizing grammar rules, but also by copying out examples, doing grammar practice exercises and writing your own sentences and paragraphs, in which you put that grammar knowledge to good use. The more you use it correctly, the more you will concrete it into your brain in the correct form, and the easier it will be to recall at the crucial moments of the test, as well as in your everyday English.