In the search for fresh investment ideas, investors tend to look at specific companies on a case-by-case basis, buying a stock whenever it looks appealing. That's the wrong approach.

Operating a vacuum like that, you may end up with a range of stocks in the same industry or subject to the same economic drivers. Instead, you should look at stocks as pieces of a puzzle. Each piece fits right in with complementary pieces, and taken together, they'll make a complete picture.

Investment advisors suggest you really need to own only eight or ten stocks to have a truly diversified portfolio. As part of that portfolio, you need at least these five holdings that give you essential exposure to key global trends:

1. Technology

From railroads and electricity to telephones and computing, stock market gains have often come from radical technological shifts. Indeed the bull market of the 1990s is directly attributable to productivity enhancements offered up by semiconductors, communications networks and web browsers.

We're in the midst of a near-term technology lull (save for the frenzy around social networking companies such as Facebook and LinkedIn), but engineers are working feverishly to come up with tomorrow's breakthrough technologies.

We don't know if these advances will come in clean energy (such as wind or solar power), industrial materials (such as nanotechnology or carbon fiber) or high-tech entertainment. So it pays to invest in both promising small companies as well as advanced technology powerhouses that conduct lots of research.

The tech powerhouse candidates: IBM (NYSE: IBM), Apple (Nasdaq: AAPL), 3M (NYSE: MMM), Texas Instruments (NYSE: TXN), Google (Nasdaq: GOOG)

2. Growing Middle Class

It's no use fretting that our children's standard of living will be no better than our current standard of living. We still have it pretty good, especially when you look at how Americans lived 100 or 200 years ago.

But you still want to focus your investments in places where living standards are rising. Countries such as China, India, and Brazil now boast of fast-growing consumer economies, and will eventually have middle classes that rival our own in terms of purchasing power.

Rising middle classes tend to spur a virtuous cycle, where rising consumption leads to thriving local eco-systems. Banks make more loans, restaurants serve more meals, governments build more roads and all this increased economic activity generates yet more wealth. So you need exposure to companies that play directly into the trend.

The global middle class enablers: Citigroup (NYSE: C), Ford Motor (NYSE: F), GE (NYSE: GE), Procter & Gamble (NYSE: PG).

Related: Employees Wanted: 10 Middle-Class Jobs That Are Actually Growing

3. Energy Exploration

Over the last few decades, geologists have been debating whether we will soon run out of oil, or have more than enough to satisfy our ever-growing appetites for energy. Both sides are wrong. Oil wells won't dry up anytime soon, but it's not likely that major new oil fields will suddenly emerge. And the oil that is left in the ground will get harder and harder to extract.

That's why companies that focus on energy exploration technology will continue to see strong demand for many years to come. These firms offer state-of-the-art seismic software that can spot untapped energy plays, extraction equipment that can reach miles down in the ocean, and other necessary tools and services to squeeze every last drop out of existing energy fields.

The energy explorers: Schlumberger (NYSE: SLB), Halliburton (NYSE: HAL), Weatherford Industries (NYSE: WFT).

4. Smart Agriculture

The world is a finite land mass. We simply can't find any more land to plant new crops to feed a population that keeps growing (recently surpassing seven billion).

So we'll have to make do with what we have, getting better crop yields from our existing farmland.

Thankfully, scientists continue to make strong contributions, coming up with new types of disease-resistant seeds, novel irrigation systems, hi-tech harvesters and inventions we haven't even heard about.

Today's R&D budgets will likely produce tomorrow's billion-dollar opportunities.

Farm belt technology candidates: Monsanto (NYSE: MON), Deere (NYSE: DE), Lindsay Corp. (NYSE: LNN), Mosaic (NYSE: MOS).

5. Entertainment

In good times or bad, people need to be entertained. And around the world, many still look to the U.S. for inspiration, from blockbuster movies and life-like video games to compelling TV shows and best-selling authors.

A careful look at the recent annual financial statements of leading U.S. purveyors of entertainment shows that foreign-derived sales are fast-growing, and hold the promise of continued strong growth for years to come.

The entertainment powerhouse candidates: Disney (NYSE: DIS), Comcast (Nasdaq: CMCSA), Viacom (NYSE: VIA/B), Time Warner (NYSE: TWX), (Nasdaq: AMZN).

The Investing Answer: With exposure to these five global trends, your portfolio can capture the most important dynamics shaping our world today and for decades to come.

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Paul has been a respected figure in the financial markets for more than two decades. Prior to starting InvestingAnswers, Paul founded and managed one of the most influential investment research firms in America, with more than 3 million monthly readers.

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