It doesn't matter if you're a growth, value, income, or momentum-focused investor -- building a successful investment portfolio takes skill, research, and a little bit of luck.How do you find the right combination of stocks that will generate returns that could fund your retirement, or your kids' college tuition, or your short- and long-term savings goals?Enter the Zacks Rank.What is the Zacks Rank?The Zacks Rank, which is a unique, proprietary stock-rating model, employs earnings estimate revisions, or changes to a company's earnings expectations, that makes building a winning portfolio easier.There are four main factors behind the Zacks Rank: Agreement, Magnitude, Upside, and Surprise.Agreement is the extent to which all brokerage analysts are revising their earnings estimates in the same direction. The greater the percentage of analysts revising their estimates higher, the better chance the stock will outperform.Magnitude is the size of the recent change in the consensus estimate for the current and next fiscal years.Upside is the difference between the most accurate estimate, which is calculated by Zacks, and the consensus estimate.Surprise is made up of a company's last few quarters' earnings per share surprises; companies with a positive earnings surprise are more likely to beat expectations in the future.Each factor is given a raw score, which is recalculated every night and compiled into the Zacks Rank. Utilizing this data, stocks are put into five different groups: Strong Buy, Buy, Hold, Sell, and Strong Sell.The Power of Institutional InvestorsThe Zacks Rank also allows individual investors, or retail investors, to benefit from the power of institutional investors.These professionals manage the trillions of dollars invested in hedge funds, mutual funds, and investment banks, and studies have shown that they can and do move the market because of the large amounts of money they invest with. Thus, the market tends to move in the same direction as institutional investors.In order to determine the fair value of a company and its shares, institutional investors design valuation models that focus on earnings and earnings estimates. Because if you raise earnings estimates, it then creates a higher fair value for a company and its stock price.Institutional investors then act on these changes in earnings estimates, typically buying stocks with rising estimates and selling those with falling estimates; an increase in earnings estimates can translate into higher stock prices and bigger gains for the investor.Because it can take a long time for an institutional investor to build a position -- sometimes weeks, if not months -- retail investors who get in at the first sign of upward revisions have a distinct advantage over these larger investors, and can benefit from the expected institutional buying that will follow.Not only can the Zacks Rank help you take advantage of trends in earnings estimate revisions, but it can also provide a way to get into stocks that are highly sought after by professionals.How to Invest with the Zacks RankThe Zacks Rank is known for transforming investment portfolios. In fact, a portfolio of Zacks Rank #1 (Strong Buy) stocks has beaten the market in 26 of the last 32 years, with an average annual return of +25.41%.Moreover, stocks with a new #1 (Strong Buy) ranking have some of the biggest profit potential, while those that fell to a #4 (Sell) or #5 (Strong Sell) have some of the worst.Let's take a look at AMN Healthcare Services (AMN), which was added to the Zacks Rank #1 list on August 9, 2022.San Diego, CA-headquartered AMN Healthcare Services, Inc. is a travel healthcare staffing company. Its business has evolved beyond traditional healthcare staffing and recruitment services, thereby becoming a strategic total talent solutions partner with its clients. It has expanded its portfolio to serve a diverse and growing set of healthcare talent-related needs. In addition to its healthcare professional staffing and recruitment services, AMN Healthcare’s suite of healthcare workforce solutions includes MSP, vendor management systems (VMS), medical language interpretation services, predictive labor analytics, workforce optimization technology and consulting, clinical labor scheduling, recruitment process outsourcing (RPO), revenue cycle solutions, credentialing software services, and virtual care management services. The company enables its clients to build, manage and optimize their healthcare talent to deliver great patient outcomes and experience.Five analysts revised their earnings estimate higher in the last 60 days for fiscal 2022, while the Zacks Consensus Estimate has increased $0.85 to $11.26 per share. AMN also boasts an average earnings surprise of 15.7%.Earnings are forecasted to see growth of 40.2% for the current fiscal year, and sales are expected to increase 28.5%.AMN has been moving higher over the past four weeks as well, up 3.2% compared to the S&P 500's loss of 8.2%.Bottom LineWith a #1 (Strong Buy) ranking, positive trend in earnings estimate revisions, and strong market momentum, AMN Healthcare Services should be on investors' shortlist.If you want even more information on the Zacks Ranks, or one of our many other investing strategies, check out the Zacks Education home page.Discover Today's Top StocksOur private Zacks #1 Rank List, based on our quantitative Zacks Rank stock-rating system, has more than doubled the S&P 500 since 1988. Applying the Zacks Rank in your own trading can boost your investing returns on your very next trade. See Today's Zacks #1 Rank List >> FREE Report: The Metaverse is Exploding! Don’t You Want to Cash In? Rising gas prices. 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Click to get this free report AMN Healthcare Services Inc (AMN): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research