If you're not going to be a junior this fall there is no reason to even be thinking about this test yet. Just focus on your classes, as this will be your best method of long-term studying.
Practice tests, practice tests, practice tests is my advice and keep taking the exam until you run out of time or make your goal. For a little extra, (when I took it anyway), you can get a copy of the test booklet and answer key when they send you your results and you can go over that and see what you missed and why.
As someone who got a 33 and 34 and worked as an ACT/SAT tutor, I can say this is by far the best way to study. Get comfortable taking full length tests, even if you're not scoring as high as you'd like. My practice tests I always got between 27-29, but I just made sure that time wouldn't be an issue on the real thing. Seeing your low reading scores are tells me that timing is probably an issue you have right now. Once you get your timing down, you can focus on issues in individual sections.
Sectional advice:
Reading: As MeSoPro said, find passages/articles of appropriate length and identify important points (author's purpose, themes, examples supporting author's argument, etc.). Work on only having to read each passage 1 time. If you have to go back and read a sentence or two, or skim something, it's no big deal. If you have to re-read an entire passage it will hurt you time-wise. Bottom line is the more you read in general, the easier this section will become.
Science: Learn how to read charts and graphs and how to understand them inside and out. What does each axis mean? What are the units and what do they measure? Are there any trends in the data? If so, what do those trends mean? In 95% of these questions the answer is literally given to you if you understand what the charts/graphs mean.
Math: Do your math homework. Seriously, there isn't a great way to study for this other than to do math problems. The higher the level of math you take, the better off you'll be because you won't have to worry about whether or not you learned the content. So if you're not a junior, this is something that will naturally improve the more math you take in hs.
English: Along with reading, this is the toughest to improve imo. Take some practice tests, then review them in depth. Look at what kinds of problems you are missing and try and see if there are any trends. Are you mixing up homonyms like there/their/they're or its/it's? Are you struggling with matching tense (past/present/future) and number (singular/plural) of your subjects and verbs? For example, you would say "his dogs are big.", not "his dogs is big" (matching the proper noun/pronoun with the verb). Do you have troubles identifying full sentences vs. clauses vs. fragments? Once you can figure out what your weakness is, you can focus on it and hopefully bring up your score. This is something that can be very difficult to do on your own, so getting help from a teacher/parent/tutor can benefit a lot here.
A 32 is tough to get, especially since you're averaging around a 23. If you take a few more practice tests, chances are you'd get around a 26ish without studying, so 32 isn't impossible, but it is going to be very difficult. If you're going to be a junior, I'd say study 3-4 hours per week seriously and be consistent. Once you're about 1-2 months away from the test increase those hours and take some more full practice tests, 3-5 should be enough to at least get you comfortable for the real deal. Good luck and don't get discouraged if you're not happy and have to retake it!