The English test gives you 45 minutes to answer 75 questions, including many that will test your ability to use punctuation and grammar correctly and to structure your sentences properly. They'll also evaluate your ability to recognize effective writing. Make sure your answers match the writing style of the questions and compare all the choices to see how they differ from each other. If something is underlined, think about how it fits into the question then reread it with your answer to make sure it works.
The reading test gives you 35 minutes to read four passages that are about 750 words long and to answer 40 questions about them. Start by underlining the main ideas in each passage while reading it so you can summarize the content. Next, think about how the sentences you underlined relate to each other. This will keep you from being overwhelmed by details as you answer the questions.
The math test gives you an hour to answer 60 questions, one minute per question. The questions are numerical problems or word problems you convert to numbers before solving and they range from pre-algebra and algebra to geometry and trigonometry. Don't look at the answer choices until you've figured out the problem, and then choose the one that matches. Since reasoning is more important than calculating for most of these questions, avoid using a calculator when you can. You should also move faster in the first part of the test, since the questions get harder later on.
The science test gives you 35 minutes to read seven passages and answer 40 questions about them. The questions in this section deal with biology, earth and space sciences, chemistry, and physics and you'll find your answers by analyzing charts, experiments, and theories. As you read the passages, write down your observations and cross out anything that's irrelevant. You should also keep an eye out for conflicting points of view and not be overly concerned with technical terms.
Since the essay test gives you just 30 minutes to write, your final product probably won't be a masterpiece. The key here is to have an essay-writing strategy you can apply to any topic before the test day arrives. Your essay should have an introduction, supporting paragraphs and a conclusion and you need to stay on topic and use examples when you can. If you write to the audience (your ACT judge), cover the criteria they're looking for and use an organized writing process (with an outline), you'll increase your chances of a high score.