Just got back from vacation and gave the Justification chapter in the LR Bible a once over. Followed up with some Cambridge Weaken and Must Be True drills. I'm aiming to get through the rest of the LR and LG Bibles within two weeks and to have another preptest by April 15.
On whether or not to use outside books such as Weston's and Walton's, I've heard some conflicting views on the boards at TLS. While those will give you a great understanding of the greater body of logic, LSAT logic is an interesting beast; it has roots in regular logic, but it also makes some assumptions that are not covered, and downright contradicted by a regular course in logic. From my experience and the experience that I can gather from others, the PS Bibles and the Manhattan books will give you a fairly comprehensive framework to attack just about every question type.
But it is interesting to talk for a minute about outside materials and considerations for a minute.
I've found that doing Sudoku regularly (paper or phone app) has helped me with LG. Work your way up to the hardest levels and get to the point where you do not have to write hypotheticals or alternatives down.
I've also tried out the Lumosity free app; I'm not sure if it works, but according to their metrics I'm improving and it costs me no money and less than five minutes a couple of times a week.
I'm also trying out learning French during my prep. I'm not sure where it is from (and take that as you will), but a study has been released that suggests that learning a new language over the course of three months resulted in people remembering 20% more new acquaintances' names than people who did not study a new language. I'll take that 20% bump when I'm trying to remember LG rules and RC passages.
Exercise is also crucial. It takes your mind off of prep for a little bit, is a great stress reliever, and results in a healthier body and mind (which in turn means that you will learn better during your prep and you will be better able to handle stress on test day). If you are a couch potato, try out the
Couch to 5k program or even just walking 15 to 20 minutes a day and ramping it up from there.
Nutrition is even more critical than exercise. I know we're all young adults here and I feel like I'm sounding like my Mom at this point, but your brain can't make the new neural pathways and myelin sheaths without some serious brain food. We're talking whole grains, nuts (walnuts, pecans, brazil nuts, cashews, hazelnuts, etc.), beans (red, kidney, black, adzuki, garbanzo), lean meats, green leafy veggies (kale, collard greens, swiss chard, spinach), and fruit. Larabars are an excellent study food when you're in a pinch and they can become your best friend. We have a lot of time here so if you don't believe me, take a month or two and eat a really clean diet (you may feel like crap for a week or two but that's just all of the junk leaving your body) and experiment with it. Also see how taking your multivitamin impacts how you feel and how you perform on PTs
Finally, don't take any of my advice blindly without trying it out for yourself first. See how you do on a section before changing up how you eat and then after you make some changes. See how you do with and without caffeine, with varying levels of sodium intake, varying levels of sleep, different amounts of clothing and room temperatures, and different levels of hunger and thirst. Once you're up to speed, take a practice test or two in different places with varying noise levels. Hell, I've even heard of people trying out having a beer or two before a preptest and they found out that they actually did better. There is a pretty entertaining thread on TLS about what kind of pencil is best for the LSAT. The moral of the story is that you should figure out what the optimum controllable conditions are and to have them every time you sit down to do a section, do a preptest, or whatever. Use those same pencils, erasers, and analog watch and be prepared for a wide range of noise levels. It may sound silly now, but your competition is paying attention to this level of detail and if you don't, you're leaving points on the table.