If you want to do well on the ACT, you need to make sure that you're ready for it. There are some specific things that you can do to help improve your chances of scoring well.
First, you should read things carefully, and that includes the main instructions, the instructions for each test, and the instructions for each question – as well as the questions themselves.
Second, you need to pace yourself. If you go too fast you may make more mistakes, but if you go too slow you won't be able to finish all of the questions.
Third, answer the easy questions out of the section you're working on first. Then go back and answer the harder ones.
Fourth, make sure you re-check your work in that section if you finish before time is up. Don't just sit there.
Fifth and lastly, ensure that you eliminate as many answers as possible from questions that you aren't sure about. Then you can make a more educated guess about the answers that are left, and you'll have a higher chance of doing well.