The Economy. In my opinion, there is nothing more important to successful investing than a general understanding of economics. If you, like most people, cringe at the thought of the subject, here's a great article by Investopedia.com that goes over the basics.

The economy tends to follow a cyclical pattern of expansion followed by slowdown or contraction. I like to try to gauge where in the economic cycle we are in order to figure out what the best industries will be to invest in. I do this by looking at economic indicators and trends. Here's a chart provided by Marketoracle.co.uk that details the economic cycle as it relates to cyclical investing. The numbers indicate the best times to buy stocks in each industry.