"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 (NYSE: BRK-B) beat the S&P 500 index in 20 out of 24 years. During that same 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 . Over the years, Berkshire has owned household names such as UPS (NYSE: UPS), Iron Mountain (NYSE: IRM), and Wal-Mart (NYSE: WMT).

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 return 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, 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.

As he recently wrote in a New York Times editorial, Buffett has been buying American stocks. The Oracle of Omaha appears to believe that the sell-off in some financials was overdone: He recently scooped up more shares of US Bancorp (NYSE: USB) when the shares set a new five-year low.

In addition, Buffett opened a brand new position in Eaton (NYSE: ETN), a Cleveland-based electrical equipment manufacturer. It's hardly an exciting business, but it generates stable free cash flow, and if Buffett likes it, there's a decent chance it's undervalued.

Another place to find great value-stock ideas is Motley Fool Inside Value. Philip Durell, the lead analyst for the service, follows an investment strategy very similar to Buffett's. He looks for undervalued companies that also have strong financials and competitive positions. This approach has allowed Philip to outperform the market since Inside Value's inception in 2004. To see his most recent stock picks, as well as the entire archive of past selections, sign up for a free 30-day trial today.

If investing in wonderful companies at fair prices is good enough for Warren Buffett -- arguably the finest investor on the planet -- it should be good enough for the rest of us.