At this point, I'd start with "Critical Care Nursing Made Incredibly Easy". I'm a fan of the Incredibly Easy books, although I hate 'for dummies' books as a rule. These offer solid nursing knowledge in an easy, gentle, introductory format. Read that, and you'll be ready for more in-depth books.
My personal favorite is "The ICU Book" by Paul Marino. Fabulous reference, our unit has one on the shelf and I have my copy at home.
One that came highly recommended but that I don't use much (just because I have Marino's book) is "Notes on ICU Nursing: Critical Care FAQ Files from the MICU" by Hammerschmidt and Mulholland.
You'll likely have some in-depth AACN modules to work on within six months of starting that will also offer you a fair bit of insight.
Best of luck, I'm sure you'll do well!