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 cha ...