Start with https://www.act.org/content/act/en/products-and-services/the-act/test-preparation/description-of-reading-test.html to see the content covered on the test.
You don't have to work in order. Start with your favorite type of passage: prose fiction, social science, humanities, and natural science. Save your least favorite type for last.
Practice reading the entire passage and then answering questions. Practice reading the questions and then skimming for the answer. See which method works best for you.
Practice pacing. It is easy to run out of time on this test.
Start with https://www.act.org/content/act/en/products-and-services/the-act/test-preparation/description-of-english-test.html to see the passage types.
Identify the most common grammar and punctuation rules. Concise answers are usually the correct answers.
Trust your ear. Read the answer in your head to see if it "sounds" correct (but don't actually say anything out loud during the test).
Don't be afraid to choose NO CHANGE.
Take as many practice tests as possible. You will be able to predict the types of questions and increase your speed on this test.