Diagnoses: the various intracranial bleeds, strokes, TBIs, SCIs (especially the C-spine ones which are more likely to be admitted to the ICU), status epilepticus, various malignancies/benign neoplasms, Guillian-Barre...
Review the physiology of the different parts of the brain and spinal cord (so you'll know what to expect for, say, a cerebellar infarct or a frontal tumor).
Also read up on brain death, and organ donation decisions following declaration of brain death.
Meds we use a lot are labetalol and hydralazine as prn's for elevated BP; nicardipine drip to lower BP, levophed drip to raise BP...sometimes we use epi also, but it seems OUR docs anyway like nicardipine or levo to start. Nimodipine is pretty common in my ICU also, esp. if there's issues w/ cerebral vasospasm. Keppra, Dilantin, Depakote for seizure prevention. Mannitol and hypertonic saline (2%, 3%, 5%, 23%) to reduce or prevent intracranial swelling. We usually use propofol or versed drips for sedation; also versed prn. We use a lot of scheduled Seroquel especially after they come off the vent but still need something to keep them calm.
Equipment: ICP monitoring: EVDs, fiberoptic monitors (my ICU uses the Camino although not as frequently as EVDs); Licox which measures oxygenation of the brain tissue; transcranial doppler studies (YOU won't be doing this; a sonographer will, but good to know about); continuous EEG...
You'll probably need hands-on experience to really get this stuff ^^^, but you could even just Google them to learn what they are, and that should help you feel more prepared.
Know that you have a huge learning curve. You will likely feel like you're drowning for a while--possibly for the next year. The veterans have been there too though, and shouldn't expect you to know it all the moment orientation ends. If you are unsure of something, ask.
This specialty can be emotionally tough. Sometimes someone will end up doing better than expected, or even just through the miracles that are modern brain care will walk out of there whole... But many will be devastated by their injury or pathology. Their FAMILIES are often devastated, and they need some good nursing too! Depending on what your personality is, especially if you tend to be a softie like I am, you'll want to figure out some self-care strategies. Actually self-care is good for everyone. This work can be stressful, even if you love it.
Congratulations again! This is a great opportunity.