It’s expensive, but I HIGHLY recommend taking a LSAT prep course from Princeton Review, or any of the other prep courses out there.
Sure, you can just buy a review book online or from a book store, but at least for me, it was much more helpful to a) have an instructor, so I wasn’t just reading, I was also listening to the lessons, etc, and b) it forced me to be accountable to the instructor and do my daily homework and take the weekly practice tests.
If you can study well on your own, and have the discipline to do the work and practice tests without an outside source holding you accountable, you might not need to go to a prep course, but I still think it’s worth it.
Additionally, like most standardized tests, the LSAT isn’t just a test, it’s a game, with a bunch of hidden rules. If you know the hidden rules of the test ahead of time, you can take advantage of them and do better. Most of the prep courses are VERY familiar with the intricacies of the LSAT and will help you game the test.
Overall, and this is just me speaking from personal experience, my LSAT scores went up a huge amount between when I took the LSAT the first time, just studying on my own, and the second time, when I went to a Princeton Review course.
Plus, the higher your LSAT score, the better the law school you can get into and the more money you might get offered.
Edited to add:
Another benefit from taking a prep course is that your practice tests are analyzed pretty deeply and they really break down which types of questions you got right and which you didn’t. As a result, while the course overall helped me, knowing what I was good at (and could focus less on) and what I wasn’t as good at and why (and could focus more on) was a HUGE help.