Understand how stock prices are determined and what stock markets do.
Know the fundamental elements of stock prices and understand how prices can get out of line with their fundamental value.
See these issues at work in the technology-laden NASDAQ in 2000.
See that bankruptcy is an important feature in corporate business but that many of the bankruptcies of 2001 and 2002 involved a level of deception on the part of their accountants that was potentially quite damaging.