I was tempted to give up after my first diagnostic test (score=141). However, that was 6 months ago, and I'm feeling pretty good about my October 4 test. Although I haven't taken a course, I've done a lot of research and formulated a study plan which has brought me to a 165 average. I expect to score 168-172 come game-day.
I would suggest skipping the December test and taking the test in 2009. In my opinion, almost everyone needs at least 6 months to properly prepare for the LSAT to achieve his/her best score. This isn't a test many people can "cram" for to do well.
My study plan went as follows:
1) Obtain every publication you can regarding the LSAT and read through the various strategies. Find what works for you and go from there.
2) Use ONLY ACTUAL LSAT QUESTIONS for practice. Although publications featuring "non-actual" questions can offer good strategies for answering questions, the "non-actual" questions can actually hinder your progress. Some of the "non-actual" questions are so poorly written that they contain mistakes; others try to confuse you with overly-ambiguous wording. As an example, I was taking a "non-actual" Reading Comprehension section and one of the questions asked "The word X, as used in line 24, would most likely mean:". However, the word X didn't appear in line 24, it appeared in line 47. WTF? Real LSAT questions don't allow these types of obvious mistakes. I've taken 7 practice LSATs under timed conditions, and here are the results: #1(actual)163, #2(actual)161, #3(actual)162, #4(non-actual)148, #5(actual)168, #6(actual)163, #7(actual)165. As you can see, my results have been pretty consistent EXCEPT for the "non-actual" test. Stay away from "non-actual" test questions; I consider them to be on par with logic spewed by my perpetually drunk uncle-in-law...
3) Phase 1 - Start your preparation section by section. Take the first ones "untimed," but allow yourself only one hour. Then, immediately review your answers and figure out which question types trouble you the most. Make sure you know not only why you got some answers wrong, but why you got the others right! Once you're comfortable, take practice sections while allowing yourself only 35 minutes. During this phase you should learn which sections are the easiest for you and which are the hardest. DON'T STRESS, YOU WILL IMPROVE!!
4) Phase 2 - Dig into the sections/question types that still give you the most problems. Figure out why they cause you problems, and then figure out how to overcome those problems. Start slowly so that you develop a sound strategy, practice that strategy, and then (and only then) work under timed conditions.
5) Phase 3 - Put it all together. Once you're comfortable with all 3 sections (Logical Reasoning, Analytical Reasoning, Reading Comprehension), start taking timed full-length practice tests.
6) Phase 4 - Home stretch. Build your endurance by taking 2 full-length practice tests per week leading up to the test, but make sure you don't burn out! You want to time your training so that when you take the actual LSAT, you're right at the peak of your ability. Don't forget to write plenty of practice essays! Enjoy them, as they allow you the most opportunity to get creative on the LSAT!
When I started studying, I was horrified by the Analytical Reasoning section. However, after 6 months of training, I actually ENJOY the "logic games" and wish that they comprised 1/2 of the test!! I have made so much improvement in this area; I took a practice test two days ago [#7(actual)165] and ACED the AR section (100% correct). Reading Comprehension is now my worst section, so that's what I'm focusing on during my home stretch. I was also miffed by comparative reasoning questions in the LR section when I started, but now I get them right nearly all the time.
I think the most important part of preparing for the LSAT is knowing your own abilities and doing everything you can to improve your weaknesses while also continuing to develop your strengths. For some people this may require hiring a private tutor, for others it may simply mean studying specific question types. Ultimately it's up to you to make the right choices; if you put in the time, this will happen. Not everyone will score a 180; however, scoring 180 does not guarantee happiness as an attorney!