I agree with @midtntutor . I am also a private tutor and I have seen marked increases in test scores. It is possible that these students could have improved their scores on their own, but because I am able to help pinpoint issues we can focus on what works for that student. I am quite sure that some of my students would simply not have been able to raise their scores as they did (17 up to 33R is my most recent student’s score) without my guidance.
Almost every student will benefit from a private tutor, of course, but the downside is that it tends to be expensive. And it may be hard to find private tutors in less built up areas away from major metropolitan centers, such as LA, NYC and Chicago. One somewhat more affordable option is Skype or FaceTime tutoring, and a number of professional test prep companies offer that option.
If that isn’t an option, I recommend giving yourself about three months from the test date and going through sections one by one to see where you need the most work. Take one test initially under timed conditions, grade yourself and see how you do. Then begin doing sections without timing, ensuring you understand what the question is asking before you try to answer. As you improve, start adding timing in again.
Get one official test prep guide, and one other well recommended guide, and read through them before launching into the testing. There are also some really great posts on CC about how testers raised their scores a lot. I have read some myself and they can be really useful. Good luck.
ETAS: please ignore the inane advice of the person above who says you should only get a tutor for math. I am a verbal-only tutor. I have just as many students as the math tutors do. Plenty of people need help in reading comprehension and English.