To prepare effectively for the ACT, you must first have a plan. It is not a good idea to simply take practice test after practice test, because that may simply reinforce bad habits. Instead, it is important to first make sure your approach to and strategy for the ACT is effective. This means knowing how to use time effectively, and knowing what kinds of questions to skip for later and what kinds of questions to come back to and check over.
Also, it is important to study any content you may not yet know or are weak in. There is only a limited amount of content that you need to actually know and memorize for the ACT, but it is important that you do study this content and be ready to apply it when you take the ACT. Once you know this content, it is just a matter of knowing how to take the ACT in the best way possible.
Most students who take the ACT do not take it in the right way, and so they waste a lot of time and end up getting a lower score than they might have gotten if they had simply approached the ACT differently.
To make sure you are as ready as you can be for the ACT, check out bestactprep.org for useful information about how to prepare for the ACT. This website not only contains helpful information about the ACT, but also offers a great ACT prep class for residents in the Champaign-Urbana area.