Well, you could try getting some discipline forced on yourself if you cannot compel yourself to sit down with the books on your own.
Taking a class can help since you are supposed to show up for the class meetings and follow along by doing the homework between classes. Since you have to put out some $$ for the class, that tends to motivate people to show up and also do the HW in order to get their monies worth because of the guilt you feel if you don't go after spending the $$.
You can also recruit people to hold you accountable. For instance, get your mom to nag you about it or get a friend or GF/BF to nag you about it. I'm sure if you make a rough study schedule, share it with your mom and ask her to check in with you frequently to keep you on track that after being unmotivated and slacking at first and then getting nagged a bunch about it that you will get down to studying to ward off the nagging and to make mommy proud!
You should make a rough study schedule for yourself.
Something like: Week 1: Go through Chapters 1 & 2 of the LGB and Chapters 1,2 & 3 of the LRB for self study or something else that conforms to the syllabus if you are taking a class.
Basically, outline some sort of a timeline plan and then start working away on it one piece at a time. It's much less overwhelming to look at it piecemeal (Week XYZ - tackle grouping games) rather than thinking about everything you have to cover in total and then getting mentally paralyzed by the total volume of work ahead of you. When you look at it one piece at a time and have it broken down into small palatable steps/tasks you are much less likely to stress out about and be discouraged by the total volume of different things you have to study and master.
When you make your rough study schedule (yes, I mean rough because you will probably not follow it perfectly and will also need to make adjustments as you go) make sure to break it down into reasonable pieces with reasonable goals within the timelines. Meaning do not set yourself up for failure by making a Superman schedule and trying to deceive yourself into thinking you are suddenly going to become the energizer Bunny.
An example of an unreasonable 'Superman' plan would be something like: "Week X, Friday - Sunday, go to library and study 8 hours each day: read entire LGB and do the homework in it" since you know you will not do that and will just end up getting mad at yourself and feel like a guilt ridden loser for not doing it.
It's much easier to start with small goals that don't require you to radically change your lifestyle. Something like making sure to fit in at least 2 hours a day, 5 days a week and then upping that as you get into the groove with more motivation and as test day gets closer. Moderation is important so that you don't dread it and avoid doing the work. Also give yourself some sort of rewards/incentives like 'after I study 2 hours today then I'll chill and watch XYZ movie'
Learn to LOVE

the LSAT! Yeah I know, easier said than done, but if you take a positive attitude towards it (and think about the rewards a great score can bring you - scholarship $$, high paying job after LS, etc.) you are much more likely to embrace it instead of hating and dreading it and trying to avoid it.