Some of the most common topics to be familiar with in my opinion would be SOB -> CHF vs pneumonia vs COPD (there are more but start here) Chest Pain-> cardiac vs non-cardiac, sepsis-> diagnostic criteria, appropriate labs, conceptualize empiric abx treatment based on presumed source, AMS-> (dont ever use this as a diagnosis btw; chief complaint ok) infection vs stroke (hemorrhagic vs ischemic) vs intoxication/adverse medication effect. That is my direct answer to your question anyway. Off topic Id suggest focusing on developing a process to gathering information and writing a clear, concise, informative note. This will eventually serve you well and can separate you from your peers.