I earned pretty good scores and I feel like almost anyone can get solid scores without exerting an inordinate amount of effort. Sometimes it's not about how hard you work, but how effectively. Here are some words of advice I wish I had about a year and a half ago:
1. I would recommend you to choose the ACT, it's a lot easier to improve your score in in my experience.
2. Buy quality materials. To be frank, most ACT/SAT study books are complete garbage. They have a lot of questions in them, but they're written by people who don't really know all that much about the ACT/SAT. In other words, most practice books do not not test the same concepts the ACT/SAT does, do not try to trick you the way the ACT/SAT does and overall simply do not accurately reflect the actual ACT/SAT. IMO the very best ACT practice book is "The Real ACT". It has a couple ACTs that were used in the past as well as the answers explained for every question. The best math study book in my experience was, and this will probably be surprising, "PSAT NMSQT Second Edition" by McGraw-Hill. It has a section where it explains every math concept in great detail that can possibly show up on the PSAT(which is very similar to the ACT/SAT). If you go through this entire section and learn everything in it, and also go over the math section of the book "Up your score ACT" 2014-2015 edition you are basically gaurenteed to get a 36 on the math section of the ACT unless your screw up and make a stupid mistake.
3. Realize how great of an investment studying for this test is. If you have a 25 right now and you study for 40 solid hours you can probably get that 25 to a 30. That can easily make the difference between getting into USNA or not, getting a scholarship or not, or getting into another selective university or not. I've read the USNA education is worth $350k. If you go from a 25 to a 30 on the ACT, your chances of getting in go up significantly, I would guess at least 10%. So for 40 hours of your time, you have just increased your odds of winning $350k by 10%, possibly even more. That's $35k for just 40 hours of your time. You might never get a job that pays that high. Treat studying for the ACT/SAT like a job, a high paying job where you earn close to or even more than $1000 an hour.
4. Start studying months prior to the test, I would say a minimum of 3 months.
5. Learn to manage your time. Skip questions that look very time consuming and put them off to the end. You're probably applying to USNA which doesn't look at reading or science, but this could help with your applications to other colleges. In the reading section if you typically struggle on a certain type of passage, do that passage last. In the science section when you get to the part where it has a bunch of scientists making different hypotheses, skip that part and come back later because it takes forever. You can miss questions and get a high score, you just can't miss very many questions. You get 1 point for the hardest question and 1 point for the easiest, so it's best to rack up all the easy points first then try and get the hard ones.
6. Understand why you are missing questions. Every mistake you make on a test happens for a reason. Figure out why you are making the mistakes and learn from it. If you don't understand why you are missing questions you will just continue to make that same mistake every time the concept pops up.
7. Spend the most time on your weakest section. For a 32 you can miss about 10% of the questions. For a 35 you can miss 1 question. It's not that hard to go from a 28->32, it's pretty hard to go from a 32->35.
8. When you take practice tests, mark every question that you aren't 100% sure that you got right. After the test, go over these questions even if you got them right. You want to be 100% confident in all of your answers.
9. You can pay like $10 or something to have your test mailed to you after you take the ACT. If you can afford it, always order this, and always go over the test. You spent 4 hours of your life on that test, you might as well learn something from it.
10. Use the internet to try and find real ACT tests that have been released. "The Real ACT" book that I mentioned earlier only has a couple tests (I think 5 or 6). Before you start taking them, study a ton. Once you take a test you can never accurately take it again because you have prior knowledge of the test. You can probably find a couple more real ACT tests online, but really make sure you make the most of each and every one of . them. There aren't very many of them for you to use, so don't waste them and start taking them without even studying. Taking 1 might not be a bad idea just to see where you are at, but don't just blow through all the tests without studying first. You'll run out of tests to take which is a huge problem.
11. This is probably my most important piece of advice to you: don't take things too seriously. This test does not determine your worth as a human being. This test does not say how smart you are. This test does not say how successful you will be in life. It's just some stupid, poorly designed test that unfortunately colleges feel is very important. That being said, sometimes you have to do stupid things to get ahead in life. This is one of those times, and this is probably one of the biggest opportunities you will have in your life. This test can change the course of your career. Take it seriously, but at the same time, realize it's not the end of the world if you don't do well on it. My brother has a friend who wasn't good at standardized tests at all, couldn't crack a 20. Because of his low scores he ended up not earning any scholarship money and elected to not go to college rather than drown himself in student loan debt. Now he works as a computer programmer and is making more than most college graduates out there. The ACT/SAT, USNA and colleges in general are just several avenues to success in life. There are many other avenues out there. It's not the end of the world if you can't do well on this test.