"It's far better to buy a wonderful company at a fair price than a fair company at a wonderful price."

If you can grasp this simple advice from Warren Buffett, you should do well as an investor. Sure, there are other investment strategies out there, but Buffett's approach is both easy to follow and demonstrably successful over more than 50 years. Why try anything else?

Two words for the efficient market hypothesis: Warren Buffett
An interesting academic study(PDF file) illustrates Buffett's amazing investment genius. From 1980 to 2003, the stock portfolio of Berkshire Hathaway beat the S&P 500 index in 20 out of 24 years. During that period, Berkshire's average annual return from its stock portfolio outperformed the index by 12 percentage points. The efficient market theory predicts that this is impossible, but the theory is clearly wrong in this case.

Buffett has delivered these outstanding returns by buying undervalued shares in great companies such as Gillette, now owned by Procter & Gamble (NYSE: PG). Over the years, Berkshire has owned household names such as Gap (NYSE: GPS), CarMax (NYSE: KMX), and Bank of America (NYSE: BAC).

Although not every pick worked out, for the most part Buffett and Berkshire have made a mint. Indeed, Buffett's investment in Gillette increased threefold during the 1990s. Who'd have guessed you could get such stratospheric returns from razors?

The devil is in the details
So buying great companies at reasonable prices can deliver solid returns for long-term investors. The challenge, of course, is identifying great companies and determining what constitutes a reasonable price.

Buffett recommends that investors look for companies that deliver outstanding returns on capital and produce substantial cash profits. He also suggests that you look for companies with a huge economic moat to protect them from competitors. You can identify companies with moats by looking for strong brands that stand alongside consistent or improving profit margins and returns on capital.

How do you determine the right buy price for shares in such companies? Buffett advises that you wait patiently for opportunities to purchase stocks at a significant discount to their intrinsic values -- as calculated by taking the present value of all future cash flows. Ultimately, he believes that "value will in time always be reflected in market price." When the market finally recognizes the true worth of your undervalued shares, you begin to earn solid returns.

Do-it-yourself outperformance
Before they can capture Buffett-like returns, beginning investors will need to develop their skills in identifying profitable companies and determining intrinsic values. In the meantime, consider looking for stock ideas among Berkshire's own holdings.

It's clear that Buffett believes health care is an attractive sector. In the second quarter, he boosted Berkshire's position in Johnson & Johnson , and the company also owns shares of GlaxoSmithKline (NYSE: GSK) and French pharma sanofi-aventis (NYSE: SNY).

However, just because a sector is attractive does not ensure success for every player. Buffett reduced his stake in health insurer UnitedHealth Group (NYSE: UNH), likely because of concerns about potential regulatory reforms.

Of course, that's the problem with following Buffett's stock picks -- we'll never know for sure why he makes the moves he does. If you're looking for another place to find great value-stock ideas -- and a clear explanation of the investment thesis -- consider taking a free trial of Motley Fool Inside Value . Philip Durell, the advisor for the service, follows an investment strategyvery similar to Buffett's. Continued...