I've used this book for an "Intro to Logic" Course. Covers formal logic pretty well. It seems like you might want something more LSAT specific, but if you're okay with just formal logic and practicing deductions and logic rules this could be useful.

http://www.amazon.com/Logic-Book-Merrie-Bergmann/dp/0078038413/ref=sr_1_1?s=books&ie=UTF8&qid=1436286691&sr=1-1&keywords=The+Logic+Book

I believe it also has kindle e-reader options.