Set aside a regular time each week to work on ACT review.
Time yourself and try to mimic ACT test conditions (no distractions, quiet environment, etc.) as you take a practice test. Will you have enough time to finish each section?
If you don't have time to take an entire test, print off the answer key and read your way through each test question. Know WHY the right answers are right, and WHY the other three answers are wrong.
If you don't know why an answer is correct, see a teacher in that content area.
Visit these sites for practice tests that are online -- you will get instant feedback on each question as soon as you provide an answer.
http://examgroup.org/act-english-practice/
http://examgroup.org/act-reading-practice/
http://examgroup.org/act-math/
Need help improving your vocabulary? Go here: http://examgroup.org/act-math/