It's always fascinating to read stories about average, everyday people who built fortunes by regularly investing small amounts over long periods of time in time-tested companies such as Merck (NYSE:MRK), 3M (NYSE:MMM), and Bristol-Myers Squibb (NYSE:BMY).

If you worked for these companies and/or regularly "trickled" money into them over the years, this is quite feasible -- Merck, 3M, and Bristol-Myers Squibb have returned roughly 14%, 13%, and 12.7% annually over the past three decades or so, respectively.

But you can also get market-beating returns by buying into great companies at more opportune times -- whenever the stock goes on sale. Rather than regularly investing small, fixed amounts, investors can use the simple method of buying a stock in portions to manage risk and boost returns. And the current market would definitely count as one of those opportune times to buy cheap stocks.

First, find a solid business
Of course, not every stock will yield such impressive gains, but big returns on investments always come on the backs of fundamentally strong businesses. And if you're confident that you've purchased shares in a great company, why wouldn't you consider buying again, particularly if the stock price is significantly below its intrinsic value? Especially in pessimistic markets (like today's), fundamentally strong businesses can be bought for good prices -- or even downright outrageously cheap.

For many large, stable companies, buying more shares when the outlook is bleak has shown to be especially rewarding. For instance, buying more Altria back at the peak of investors' pessimism over tobacco lawsuits would have juiced your returns considerably. Investors have gained more than 690% from its low in 2000, including the benefits gained by spinoffs of Kraft Foods (NYSE:KFT) and Philip Morris International.

For younger, riskier companies, a strategy of acquiring shares in portions is a smart play. It limits your initial outlay and reduces your exposure to significant drops, should the company falter or broader economic conditions change.

For example, look at Mobile Mini. You've probably seen the company's portable storage units around construction sites and parks -- the firm converts shipping containers into storage lockers, and then leases them for use in commercial and residential markets. From 1997 to the beginning of 2002, Mobile Mini's stock soared nearly tenfold as the company capitalized on rising demand for storage units. Then, in an abrupt six-month period, the stock shed roughly 70% of its value.

When demand for portable units dropped with the slowing economy, margins began to shrink, and investors poured out of Mobile Mini stock. But the fundamental business operations remained intact. Investors who took advantage of this and put money into Mobile Mini stock when the outlook was bleak now show more than a 200% gain on that added investment. The larger economic conditions had only a temporary impact on Mobile Mini's solid business model.

Buy again
Other strong performers, such as Celgene (NASDAQ:CELG), Boeing (NYSE:BA), and (NASDAQ:CRM) have experienced big drops in share price at some point, only to come roaring back. Investors who focused on the underlying businesses, rather than the stock prices, were more likely to turn the event into an opportunity.

The final caveat with this method is to ensure that you aren't throwing good money at a truly deteriorating company -- hence the importance of understanding the underlying business. In their Motley Fool Stock Advisor service, David and Tom Gardner track all of their investments and re-recommend promising companies when the price is right.

This article was originally published Feb. 12, 2007. It has been updated.

Fool contributor Dave Mock buys pogs again and again -- more for sentimental than intrinsic value. He owns shares of 3M, which is also an Inside Value selection. is a Rule Breakers selection. The Motley Fool's disclosure policy keeps a shopping list handy.