Once you have chosen which ACT test(s) to take, you should register for the exam ASAP. Go to act.org and set up a student account. Then click on “Registration” scroll down to “Dates, Locations, and Fees” where you will find a list of dates for “Regular Registration Deadline” and for “Late Registration Deadline.” Should you miss the Late Registration Deadline, you can still potentially sign up for the test by scrolling further down to “Standby Testing.” Please note that you must register for Standby Testing and that this type of testing also comes with its own deadline.
You should also take the test at a quiet high quality test center—not all test centers adhere to the highest standards. In this regard, be aware that the best test centers—for example, in New York City, the NYU test center is very popular with students—fill up very quickly.
If you find that the test center you would like to test at is already filled up, or if you prefer to take the ACT on Sunday, go to act.org and type in “Show non-Saturday Test Centers.”