Reddit mentions of Ultimate Guide to the Math ACT

In all honesty, you don't need big-name practice workbooks (PR, Barron's, Kaplan, etc.) to do well on the exam. Take as many of the ACT practice tests (the real ones, skypetutor has a link on reddit), and each time you miss a question, be sure to review what you got wrong. For English, if you're a beginner, study the ACT English bootcamp: https://www.youtube.com/watch?v=p9-UcKc39-U&list=PLWrx3HAZbAqGTrgoMjihz1tHLdhJ3YwdR

For math, I would recommend Richard Corn's book on the ACT math section: https://www.amazon.com/Ultimate-Guide-Math-Richard-Corn/dp/0998584916/ref=sr_1_fkmr0_2?s=books&ie=UTF8&qid=1537652751&sr=1-2-fkmr0&keywords=ultimate+guide+to+the+math+ACT+2nd

He gives a really good explanation of all the concepts on the ACT math section and even includes practice questions.

For reading, I would recommend you just grind as many of the practice tests as possible. Also remember, one of the answer choices is 100% correct, while the three others are 0% correct. In other words, one of the questions is completely, without a doubt, correct, while the others contain something that is completely wrong.

For science, I would recommend you grind as many practice tests since this section is similar to the Reading section, but I would also recommend For the Love of ACT Science by Michael Cerro, found here: https://www.amazon.com/Love-ACT-Science-innovative-standardized/dp/0996832203/ref=sr_1_1?s=books&ie=UTF8&qid=1537652960&sr=1-1&keywords=for+the+love+of+act+science

He gives a thorough review of ALL types of questions on the test, and even includes several practice tests that are based off of the real exams.

I will stress this one more time, NOTHING BEATS PRACTICE WITH A REAL ACT TEST. Don't spend 30 dollars off on Amazon to buy a Princeton Review or Barron's practice book with only 3-4 practice tests. There are over 70 real tests on reddit, courtesy of skypetutor: https://www.reddit.com/r/ACT/comments/8l7xhc/links_to_free_pdf_downloads_of_all_65_and/