How to increase ACT SCORe by 6-8 points

I have taken the ACT about 4 times and I always got a 17 on all 4. I study pretty hard. I really need some advice and help? How can I study better to increase my score by 6-8 points.
English- 16
Math- 23
Reading -17
Science-21
Please give me some advice!

If you aren’t already, do practice tests. Do only one section, for example, if you are having trouble in english, work on just english sections. For English, you should definitely read up on punctuation use (I believe there is a page on sparknotes about it if you look up ACT punctuation). I’ve been using the red book for practice, since it is probably the most accurate book. It also comes with explanations to all of the problems, so when practicing, make sure you read through the explanations for the mistakes you make, and make sure you clearly understand why the answer is what it is. If you are struggling with timing, you may want to slowly go through a section first before trying to speed up. It may help if you give yourself enough time to thoroughly think through your answers once or twice before trying to do it quickly.

From your screen name, I’m going to guess that English is not your first language. Even if it is, your English and reading scores indicate that those skills need improvement. Rather than studying and memorizing grammar rules, I would recommend reading English literature so that your brain can incorporate the language.