Many people recommend
this book.
There's also a list of 'topics' for the exam on the red hat website. The best way to prepare for it is to set up 2-3 machines and practise.
Also you need to practise a lot. Did I already mention that you need to practise? No?! So, I'm doing it now: You need to practise a lot.
Time is an important factor on such an exam, so you need to be able to do all those things with your eyes closed
btw, there are a lot of threads on this topic here on this forum. Search for them.