Successful investing demands that investors constantly supply themselves with information. Because the business world is always changing, you can never learn too much. Just look at the newspaper industry. Who could have predicted that the Internet would come along and permanently alter the economics of that entire sector? If you want to be an effective investor, you need to keep up with those twists and turns and never stop educating yourself.

Turn those pages
Thinking independently is the greatest attribute an investor can have. To think independently, you need to expose yourself to a variety of sources. And to do that, you have to read. A lot. The Wall Street Journal is one excellent source that you should read every day. But that just scratches the surface. Fine periodicals such as Barron's, Business Week, The Financial Times, The Economist, and others will further enrich you with their independent perspectives, as will online sources such as Value Line and, of course, The Motley Fool.

After that, the real fun begins: annual reports. There is no substitute for the information you gain from reading them. Not only will they educate you about a particular company, but they'll also give you insight into industries, their managements, and entire perspectives on how various businesses operate.

You'll always have more reading to do than available time, since there are literally thousands of annual reports out there, but full-time investors should make a habit of reading at least a couple of reports a day. Keep it up for a few years, and you'll begin to develop a mental model of businesses and industries.

Must-read annuals
Although spending time with any annual report will yield value, there are a few you must read, without exception. The most obvious one is the Berkshire Hathaway report, written by Warren Buffett himself. Buffett has read thousands of annual reports in his lifetime and knows more about business than just about anyone else does. And given Berkshire's investments in major companies like Coca-Cola (NYSE:KO), Wells Fargo (NYSE:WFC), and ConocoPhillips (NYSE:COP), you get commentary on a bunch of different sectors in a single report.

Equally important, I think, is the annual report from Wal-Mart (NYSE:WMT), the world's dominant retailer. The company logged more than $400 billion in sales in fiscal 2009, and it has more than $30 billion of inventory in everyday household products alone. Just by looking at Wal-Mart's report, you can spot some consumer-spending trends that can serve as a microcosm of the entire economy. After all, Wal-Mart literally sells more products than many small nations do.

Also on the must-read list is General Electric's (NYSE:GE) annual report. GE is involved in a wide array of industries that exert a significant influence on various other industries all over the world. And given its financial challenges recently, it can also give you a glimpse onto the front lines of the credit crunch.

Finally, make sure you get a good sampling of other major global companies, such as ArcelorMittal (NYSE:MT), and Cemex (NYSE:CX). Besides teaching you a little bit about steel, and cement, these companies' annual reports will provide a rich source of industry data and global economic statistics.

Always be prepared
The Internet reshaped the newspaper industry, but it has also helped reduce the time required to access information. However, you still have to apply the effort to dig in and learn. There are no shortcuts. The bright side is that the payoff from all this work is enormous.

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Cemex is a Motley Fool Global Gains recommendation. Coca-Cola is a Motley Fool Income Investor selection. Berkshire Hathaway, Coca-Cola, and Wal-Mart are Motley Fool Inside Value recommendations. Berkshire Hathaway and Cemex are Motley Fool Stock Advisor recommendations. The Fool owns shares of Berkshire Hathaway and Cemex. Try any of our Foolish newsletters today, free for 30 days.

This article, written by Sham Gad, was originally published on Jan. 31, 2008. It has been updated by Dan Caplinger, who owns shares of Berkshire Hathaway, General Electric, and ArcelorMittal. The Fool has an intelligent disclosure policy.