Grammar is no longer tested directly on the TOEFL. But you should understand, grammar is not only one of the topics we should learn to pass the exam and then just forget. Grammar is the system of the language, the way all word-combinations, sentences and different constructions should be built. Without knowing or with poor knowing of grammar you can not use the language correctly.
Your grammar will be obvious in your speech and writing. Using a wide range of different grammatical constructions enriches your language.
For fulfilling tasks from all sections you have a short time. So you’d better know the material well to read, catch the information, speak and write fast, to feel comfortable in any task and in any topic. For example, in each of the six tasks in the speaking section, you have to express your ideas on a given topic for one minute. Though time is short, you rather be able to speak confidently, expressing your ideas clearly and without obvious grammatical errors.
According to the speaking rubrics, published by ETS, a student should “demonstrate effective use of grammar” and “exhibit a high degree of automaticity, with good control of basic and complex structures.”
Writing your essay you’ll have another chance to demonstrate your grammar abilities. This section is one which “displays consistent facility in the use of the language, demonstrating syntactic variety, appropriate word choice, and idomaticity, though it may have minor lexical or grammatical errors.”
To improve your grammar use different books and study both theoretical material and examples, do grammar exercises.
The most important grammar points
verb tenses, nouns, pronouns, modals, parts of a sentence, verbs, prepositions, gerunds, infinitives, articles, noun clauses, adjective clauses, adverb clauses, prepositional phrases, comparatives, superlatives, conjunctions, connectives.
Be sure using parallel structures, word order, word forms, word choice and redundancy in your speech is correct.