I used "LPIC-1 Sicher zur erfolgreichen Linux-Zertifizierung" by Harald Maaßen, published by Rheinwerk Computing (in German), ISBN 978-3-8362-6375-7,v and I liked it quite a lot.
There's quite a few of these books, also in English, and they're all kinda useful.
I work at a large scientific library, so I used it quite a lot to get me a selection of LPIC books. Also, I usually not just read the book, but I had my computer with me, so I could a) try things out that were discussed in the book and b) read up the whole (!) man page of any command used in the book. I found that that helped me quite a lot, because it gives you an opportunity to tinker and practice.