You'll never forget 2008. But if you're lucky, what you learn from the worst year for stocks in your lifetime will help you earn more from your portfolio for decades to come.

The volatile moves in the markets have made it hard to get any kind of long-term perspective. When the Dow skyrockets 900 points one day only to drop 700 a couple days later, and when household names like Fannie Mae (NYSE:FNM) and AIG appear close to collapse, you can barely think ahead to next week -- let alone a retirement date that may be 20 years or more away. But before we reach the end of 2008, you should try to take a step back and look at some of the trends you've seen this year.

Tip 1: Look past stocks for real diversification.
You've heard plenty about the benefits of having a diversified portfolio. The key premise behind diversification is that when some stocks go down, others go up, and so owning a little of both will keep your overall portfolio from falling as far.

Unfortunately, that didn't work so well this year. Sure, investors who correctly foresaw the worse-than-expected problems for financial stocks like Citigroup (NYSE:C) and Goldman Sachs (NYSE:GS) dodged a big bullet. But while financials were at the epicenter of the crisis, most other sectors didn't emerge unscathed.

For instance, former highfliers like natural gas giant Chesapeake Energy (NYSE:CHK) and commodity play PotashCorp (NYSE:POT) couldn't sustain their sharp gains in recent years and came tumbling back to earth. Similarly, emerging market stocks like Petrobras (NYSE:PBR) also disappointed investors who looked for foreign stocks to decouple from a U.S. bear market.

Meanwhile, Treasury bonds had a great year, helping to avert a complete collapse in net worth for many investors. That's a good reminder to own a variety of assets if you really want to be diversified.

Tip 2: Markets can always go further than you think.
The entire stock market down 40% in a single year? 30-year Treasury yields below 3%? Few would have thought such things were possible, let alone that we'd see them both happen at the same time.

Yet throughout history, markets have extended themselves well beyond where you'd think they'd snap back. How many investors shorted fad shoemaker Crocs (NASDAQ:CROX) during 2006 and 2007, only to have to cover at higher prices as the stock reached $75 and higher? Now, the stock trades for just over a buck. And this time last year, who would have guessed that oil prices would go up toward $150 -- or come crashing down below $40 just months later?

The key here is that you can't rely on the market to validate your investing decisions for you. Instead, you have to have the conviction of your own beliefs, even if the market goes against you at first. Only by having an independent basis for picking a stock will you keep yourself from getting whipsawed by every crosscurrent in the markets.

Tip 3: We've seen the worst.
No, I'm not saying that the bear market is over, or that everything's going to be fine from here on out. I expect things to get somewhat worse before they get better -- and I'm hoping to find deals like the ones that popped up in recent weeks.

What I do mean, though, is that like warriors after their first battle, we've all been bloodied by the market -- and we're all market veterans now. Before this year, many of us never knew what we'd do in a bear market that's this bad. Now, though, we've gone through a real-life crash test -- and we know how we reacted. Regardless of how you did, that experience will help guide you through similar rough patches in the future.

Of course, we may not be through this rough patch yet. But by keeping these tips in mind, you'll regain a long-term perspective that will let you evaluate your investing strategy in a more constructive light. That way, you'll keep learning and becoming a better investor -- no matter what roadblocks the market may put in your path in 2009 and beyond.

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Fool contributor Dan Caplinger wishes everyone an early and prosperous new year. He owns shares of Chesapeake Energy. Crocs is a former Motley Fool Hidden Gems Pay Dirt pick. Petrobras is a Motley Fool Income Investor recommendation. Chesapeake Energy is a Motley Fool Inside Value pick. Try any of our Foolish newsletters today, free for 30 days. The Fool's disclosure policy never asks you for a tip.