I found the best way to learn is from caring for different types of patients. Usually, as a new ICU you are give progressively more challenging patients over time. Initially, your patients might be the more stable or chronic. This method allows you to develop your assessment and organzational skills. As you get the hang of it, you will get more unstable patients. As far as reference material, there are a number of great books. You can join the local chapter of AACN, which offer educational opportunities. Two years after graduation, I studied and passed the CCRN certification test. I did because I wanted to learn more. CCRN Study books cover the essential areas which are great to know. Some doctors are great teachers when they feel like it.
Its initially very overwhelming but it gets better with time and experience.
Best wishes for you success,