If you've done four or five practice tests and see no improvement, then you've hit a score plateau. Two common approaches to overcoming score plateaus: 1) Buy all the LSAT books you can and go through all of them searching for some hidden gem. 2) Keep taking more practice tests. test-preparation.net suggests that you do neither. It's unlikely that you're going to find some hidden gem, indeed, it's likely that you'll end up confused because many LSAT preparation books often contain similar strategies yet use different terms for those strategies. Don't keep taking more tests because you'll simply repeat whatever problem it is that you now have, while depleting valuable real practice LSAT material. Try the following:
Identify the exact problem(s)
What exactly is your problem? Is it understanding? A specific question type? A particular section? Timing? Pacing? Mental endurance? Don't assume that it's necessarily understanding the material. You may be able to gain a significant score increases by changing other factors.
Get back to the basics
Many LSAT test-takers hit score plateaus after significant study and practice, and to overcome the plateau, try to work on the most difficult question types. If you are trying to get from a 175 to a 178, then this probably is a good plan. However, if you're in the 150s and trying to reach the 160s, then you may be better off reviewing the basics of logic to ensure that you have complete understanding, and can analyze logical structures quickly without getting bogged down by content. LSAT test-takers often focus on only doing LSAT practice tests, but remember that the LSAT did not invent logic, and you can, and should, study the basics of logic outside of the LSAT. test-preparation.net suggests that you either take a basic logic course, or read Richard Feldman's Reason & Argument, Chapters One through Ten.
Join an LSAT study group
One of the best ways to learn is to teach. Try to find an LSAT study group that is just starting out, and help out those who were in your shoes not too long ago. You'll likely be surprised at the clarity you gain after you have taken the time to explain it to others. If there's noone in your area, check out www.lawschooldiscussion.org
Get a tutor
If you're unable to see what your problem areas are, consider getting a private tutor, even if only for a few hours. If you've done significant study and practice, then a good LSAT tutor will be able to identify your weaknesses within a few hours (although helping you to overcome those weaknesses may take longer). When searching for a tutor, though, demand the best. Find one with experience -- a minimum of one year teaching the LSAT.
Try writing mock LSAT questions
LSAT test-takers avoid any "fake" LSAT questions like the plague. However, a great way to better understand the test is to try your hand at writing it. By doing so, you start to understand what's going on the minds of the writers of the LSAT, and will be able to see how passages, question stems, and answer choices are structured, and the similarities that exist from test to test. Try writing really tricky questions similar to those that have tripped you up. Note: Neither you nor anyone else should actually practice on these questions that you write -- the purpose is for your own understanding.