Surveys show that many Americans haven't amassed the wealth they will need to provide for the lifestyle they want to live during retirement.

CNBC offers six tips to enhance your retirement portfolio so that you aren't one of them.

1. "Figure out what you need." You should determine how much money you will spend in retirement and estimate much you need to save to provide that income.

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2. "Save more, and extend your working life." The more you save, the more you'll have to spend. Working longer obviously adds to your wealth.

3. "Diversify." Stocking your portfolio with different asset classes can curb your volatility and limit your losses in times of trouble.

4. "Design your asset allocation with an eye to taxes." In general, it makes more sense to keep stocks in your retirement portfolio, as you will save on taxes when you buy and sell as you rebalance.

5. "Keep a healthy portion of equities." Just because you're getting older doesn't mean that you won't need the higher returns that stocks historically provide.

6. "Relax and set yourself up for automatic rebalancing." Rebalancing will keep your allocations to stocks and bonds at the levels you have chosen in order to maximize your returns during retirement.

One factor to keep in mind is investment fees. And when it comes to 401(k) fund fees, the findings of a recent study from law professors Ian Ayres of Yale University and Quinn Curtis of the University of Virginia will trouble 401(k) investors.

The duo looked at more than 3,000 401(k) plans and found that on average participants paid almost a percentage point more in annual fees than investors in low-cost index funds available to the general public, The Wall Street Journal reports.

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