In 2008 and 2009, the dividend landscape was turned upside-down. During the fourth quarter of 2008 alone, 288 companies cut payouts. Not to be outdone, according to Standard & Poor's, another 804 dividend payments were cut by public companies in 2009 -- costing investors another $58 billion.

Nevertheless, amid all the dividend cuts and suspensions of the past two years, we were reminded of five key lessons that we can use to our advantage going forward.

Lesson 1: Stock dividends are a privilege, not a right
The first and most obvious lesson -- that dividends are not guaranteed -- was also a truism most people ignored in the years leading up to the dividend crisis. But unlike interest from bonds and CDs, a company's board of directors must choose whether or not to pay out cash dividends to shareholders.

There are obvious incentives for a board to maintain or increase regular dividend payouts -- it helps attract income-minded investors and is a sign of financial strength -- but in times of severe uncertainty, particularly in a credit-driven panic like we had, cutting the dividend to raise or preserve cash becomes a more attractive option for companies. This is exactly what Pfizer (NYSE:PFE) did last January, when it cut its dividend in half to fund its acquisition of Wyeth.

When one company cuts its dividend, it usually signals an inability to manage its finances. That cut becomes a scarlet letter for the firm. As we saw over the past two years, however, if many companies are in the same boat, the stigma of a cut is lessened, making it a more attractive option for cash-strapped boards.

Lesson 2: Beware of chasing high yields
Over the past decade, with interest rates and market yields relatively low, income-thirsty investors were forced to go further up the risk ladder to find agreeable yields -- and many have paid the price.

During the last bull market, for example, people piled into real-estate investment trusts (REITs), which were paying out handsomely on the back of the real estate boom. When properties stopped generating as much money, through broken contracts, unleased space, or lessees behind on their rent, the dividends took the hit. A number of REITs, like apartment-owner Equity Residential and shopping mall operator Simon Property Group, had to cut their payouts last year.

A good rule of thumb is to be skeptical of any dividend yield more than two-and-a-half times the broader market average (currently 2%, so be wary of 5%-plus). Anything over that amount implies that either the market has concerns about the company's ability to grow, or the stock price has fallen sharply for good reason.

In June 2008, for instance, Bank of America (NYSE:BAC) had a yield greater than 10%, at a time when the market average was around 2%-3% -- a good indication that the dividend was anything but assured. Sadly, it was not.

Lesson 3: Focus on cash, not earnings
While earnings are an accountant's opinion, cash is fact. Without enough actual cash to pay the dividend, the company must fund it with either debt or by selling stock -- neither of which is sustainable.

To determine whether or not a dividend is sustainable, first look at cash flow from operations going back five years or more. Then subtract capital expenditures from each of those years. Whatever is left over can be considered "free cash flow," which the company can use to pay dividends or repurchase shares.

Next, look further down the cash flow statement and see how much the firm paid in cash dividends each year. If that figure is consistently less than free cash flow, it's a good sign that the firm has enough cash to maintain its current dividend. Three names that fit this bill today are:

Company

Dividend Yield

Free Cash Flow Payout Ratio

Procter & Gamble (NYSE:PG)

2.9%

40%

McDonalds (NYSE:MCD)

3.5%

58%

Lockheed Martin

3.3%

23%

*Data provided by Capital IQ, as of Jan. 25, 2010.

Lesson 4: Diversification still matters
While many sectors experienced dividend cuts over the past two years, none were hurt as much as the financial sector, which at one point made up 30% of all dividend income from S&P 500 members. That's now down to 9%, according to S&P analyst Howard Silverblatt. But despite the gloom in financials, 33 of the 34 dividend actions taken by consumer staples stocks in the S&P 500 last year were positive.

A dividend-focused portfolio that was diversified across sectors still likely took a hit during the financial crisis, but less so than one heavily exposed to financial stocks for their higher yields. That's why sector diversification matters, even if you need to sacrifice a little yield in the near-term.

Lesson 5: Selectivity is paramount
Because dividend cuts can be wide-ranging during a financial crisis, your best bet is to hand-select a diversified group of strong dividend payers, rather than assuming that dividend-themed indexes and ETFs will save you.

For example, in December 2008, the dividend-weighted WisdomTree Equity Income ETF was heavily invested in General Electric (NYSE:GE), US Bancorp (NYSE:USB), and Wells Fargo (NYSE:WFC), all of which slashed their payouts in coming months.

To make matters worse, since the ETF is only allowed to rebalance once per year, owners of the ETF were forced to hold many stocks that either stopped paying dividends or drastically reduced their payouts until the ETF was allowed to rebalance.

Wrapping it up
The five keys to successful dividend investing will help you build a diversified portfolio of hand-selected dividend payers with above-average but modest yields, well-covered by plenty of free cash flow. Pair this group with high-quality investment-grade bonds and a smattering of REITs, and you'll have built yourself a well-rounded income-focused portfolio that can help you achieve solid profits without undue risk.

If you'd like help getting started with this strategy, our Motley Fool Income Investor service can help. Advisor James Early and his team have assembled a group of stocks with an average yield of 4.1% and provide valuations and risk ratings for each recommendation. You can start your free, 30-day trial to Income Investor by clicking here.

Fool analyst Todd Wenning recommends Salt: A World History by Mark Kurlansky for fellow history geeks. He owns shares of Procter & Gamble, an Income Investor recommendation. Pfizer is a Motley Fool Inside Value selection. The Fool owns shares of Procter & Gamble and has a disclosure policy.