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A year ago, investors were dealing with heavy losses from the most brutal stock-market selloffs in years. The last thing they expected was a ferocious bull market. And yet, shares soon began to soar -- climbing more than 50%.

Last year's unexpected stock rebound -- and the sudden selloff last week -- should remind investors to be on the lookout for the next surprise. That's because big profits come in being early to the next trend, and in preparing for the next downturn.

It's a simple rule of thumb: Buy before the good news; sell before the bad. The tricky part comes, of course, from guessing where the news might break to begin with.

Here are some places to watch:

Energy Boost: Many analysts expect energy prices to keep climbing, as demand from China pushes oil prices higher. But Mr. O'Rourke says crude prices could actually drop below $50 a barrel this year, helping to fuel an economic recovery.

Heady Growth: Most economists predict subpar growth in the U.S. and around the globe in 2010. Consumers are dealing with too much debt, help from government spending will peter out, and businesses aren't spending much. But if the recovery conforms to historic patterns after major downturns, it could be surprisingly strong.

Growing Greenback: There are reasons to expect a dollar rebound. Worries about the debt of European nations took hold last week, pulling down the euro and sending skittish investors back to the U.S. dollar. Gold and commodities fell, too.

If U.S. growth proves stronger than expected, the Federal Reserve could signal an interest-rate increase, which also would help the dollar and weigh on shares of gold miners and other commodity producers.

Health-Care Recovers: Health-care stocks were haunted by the specter of President Obama's overhaul plans, though the shares have generally held up. In recent days, they've been hit by downbeat earnings -- such as last week's quarterly results from Pfizer, which helped send the drug maker's share price down 5% over two days.

But some of these shares could see healthy gains. Merck, for example, trades at price/earnings multiples that are below the overall market, yet sports a hefty dividend yield of nearly 4%. If the stock market turns rocky (and it certainly did last week), those dividends will look more attractive.

Health-care companies may have an easier time raising prices if the government can't settle on an overhaul plan, some analysts say.