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 companies such as Home Depot (NYSE:HD), Caterpillar (NYSE:CAT), and McDonald's.

If you worked for these companies and/or regularly "trickled" money into them over the years, this is quite feasible -- Home Depot, Caterpillar, and McDonald's have returned roughly 15.6%, 11.2%, and 12.2% annually over the past two decades or so, respectively -- even after taking into account the significant losses Home Depot and Caterpillar have seen in the past few years.

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 now would definitely count as one of those opportune times to buy cheap stocks.

First, find a solid business
Of course, every situation is different, 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 intrinsic value? Especially in pessimistic markets (like today's), fundamentally strong businesses can be bought for good prices -- or even downright outrageously cheap.

For large, stable companies, buying more shares when the outlook for them is bleak can be especially rewarding. For instance, buying more British American Tobacco back when investors' pessimism over tobacco lawsuits was at its peak would have juiced your returns considerably -- the stock has returned nearly 1,200% from its low in 2000.

In a more recent example, stock in wireless technology giant Qualcomm (NASDAQ:QCOM) traded flat for nearly two years as major legal disputes with Nokia (NYSE:NOK) weighed on shares despite continued, fundamental growth at the firm. Once the dispute was settled, Qualcomm's stock jumped more than 25% in a few days as the pessimism melted away.

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 its portable storage units around construction sites and parks -- the company 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 soared nearly tenfold as it capitalized on rising demand for storage units. Then, in an abrupt six-month period afterward, 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. Even investors who bought at the peak but continued to hold the stock have still matched the broader market return.

But money invested when the outlook was bleak is now up more than 250%. The larger economic conditions had only a temporary impact on Mobile Mini's solid business model.

Buy again
Other companies, such as Garmin (NASDAQ:GRMN), j2 Global (NASDAQ:JCOM), and Intuitive Surgical (NASDAQ:ISRG) 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.

If you'd like to see which stocks they recommend you buy again -- and again and again -- you can click here and get a 30-day trial of the service for free.

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 Garmin, Qualcomm and Mobile Mini and is author of The Qualcomm Equation. Intuitive Surgical is a Rule Breakers pick. The Home Depot and Nokia are Inside Value recommendations. Garmin is a Global Gains recommendation. Mobile Mini is a Stock Advisor selection. The Motley Fool's disclosure policy keeps a shopping list handy.