Show up early so you have plenty of time to collect information. Be meticulous, know vitals from overnight, labs and their trends, Is/Os, ventilator settings, and medications on your patients. Do thorough exams on patients. Know the patient's code status and proxies. Maintain a good rep with family members so that they will trust you when the time comes to make difficult medical/ethical decisions. Earn the trust of your nursing staff as well - they will likely know more than you when you first start out, so respect their input - they will in turn, make your life easier.
Learn common procedures: indications, complications, technique. Central venous catheters (especially subclavian and femoral), arterial line insertion, lumbar punctures should be your priorities to learn. Eventually, if you have some helpful NSGY residents or attending, EVDs.
Learn your pressors and their indications.
Read. Read. Read. Including the guidelines.
Hold on to your butts.
The best advice I ever got: "You'll be alright."