I am constantly reading business and investment books, I can't get enough of them. At the moment I'm reading Peter Lynch's 'Beating the Street' for the second time. I would highly recomend it for anyone interested in investing. He managed the Fidelity Magellan Fund in the 90's and was considered the worlds number 1 fund manager at the time.
In the book he passes on some of his ideas and principles, what he calls 'Peters Principles', which although they seem very simple, are actually very insightful. They seem even more relevent today than back in 1994, when the book was written. There are 21 in total but here are some examples,
Never invest in any idea you can't illustrate with a Crayon. What he is getting at here is that you should understand the company or fund you are investing in fully, and it should make basic business sense
You can't see the future through a rearview mirror. This one is simple, past performance is not a reliable guide to future returns. What did well last year, may not do well this year.
Everyone has the brainpower to many money in equities, not everyone has the stomach. This has been proven over the past 2 years, with massive panic selling in 2008, and a massive rebound in the markets in 2009, which only those who stayed in benefited from.