Honestly, I'm not bad at writing so I don't plan on 'really' preparing for this section. It's important to remember that it is not marked. If you are planning on studying, I would take a look at some previous writing sections and be able to write a compelling argument.
I know it's probably not much help but hopefully JY can help you a bit more!
I would agree with Kyle; this is one of my stronger areas so it will not require nearly as much preparation. Having said that, I believe it is good practice to see how they expect it structured and to practice a few 2 page essays based on the criteria. Usually, if I recall, it is based on arguing in favor of some position given a set of criteria.
The writing section is not part of the LSAT score so I wouldn't bother spending time studying for it. That being said, I also wouldn't leave the writing section blank. Just look at 2 or 3 writing samples to get a feel for what to expect.
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I know it's probably not much help but hopefully JY can help you a bit more!
http://7sage.com/discussion/#/discussion/69/so-about-that-writing-sample