4. Watch those fees

Last summer, you should have received a statement from your plan administrator that listed plan investments and their performance, the types of expenses that can be deducted from your account, and the oper­ating expenses for each investment. That was followed by another statement spelling out which fees you rang up yourself -- say, for setting up a loan.

Fees can have a dramatic effect on your retirement savings, so if you tossed the statements in a drawer, fish them out. You can get an idea of how the overall fees for your plan compare with those of similar plans at other companies by going to BrightScope.com. If you don't like what you see, talk to your plan manager about making changes. As for the fees for your particular investments, you might discover that another investment among your options costs less and has turned in comparable returns or better. In that case, it makes sense to switch.

5. Save in a Roth 401k

If your company's 401k plan offers a Roth option, you have a tough decision to make. As with a Roth IRA, a Roth 401k involves trading a tax break today for a tax break in retirement. Salary you steer into a Roth account is not pretax. If you contribute $1,000 a month, your take-home pay really goes down by $1,000 -- not the $750 it would cost you to contribute to a traditional 401k if you're in the 25% federal tax bracket (or less if you're also avoiding a state income tax). But the payoff is sweet. Inside the Roth account, all earnings are tax-free, not simply tax-deferred. Assuming the account has been open at least five years, withdrawals in retirement are tax-free.

If you expect to be in a higher tax bracket in retirement, a Roth is sure to be a winner. You pay tax on deposits at a lower rate than you'd owe on the withdrawals. If you expect to be in a lower bracket, or you need the tax break now, the Roth account becomes less tempting. But keep in mind that the more taxes you pay upfront, the more money you'll have to spend as you please in retirement.

Choosing the Roth is not all-or-nothing. You can divide your contributions between traditional and Roth accounts in any way you like and change the mix at any time. If your company matches pay-ins, those funds automatically go into the traditional account.

Early this year, Congress greatly expanded the opportunity for workers to convert all or part of their traditional 401k account to a Roth 401k, if their company offers the option. As with IRA conversions, the price of admission is the tax you'll pay on every dollar you move to the Roth.

6. Build your own pension

When you retire, you have the option of using some of your 401k assets to purchase an immediate fixed annuity to provide a steady income. Now, some employers are offering an annuity within their 401k that protects your savings in the years before retirement and guarantees lifetime income after you've retired.

With an immediate fixed annuity, the monthly payout is based on how much you put in -- say, $100,000 -- at the time you buy it. With the newer annuities, known as guaranteed lifetime withdrawal benefits, you would invest that $100,000 in an insured product -- typically, a target-date fund -- that guarantees a base amount from that point forward. The guaranteed amount is your $100,000 buy-in plus contributions you make later and any earnings on your investment, minus expenses. The base amount can go up, but it never drops below the high-water mark in the years before you retire, even if your investments do poorly.

You'll pay for that peace of mind. The cost of the guarantee -- perhaps 1% of your balance a year, plus investment expenses -- means the guaranteed amount won't grow as fast as the same amount in an account without the guarantee. And the annual payout -- about 5% of the balance -- is less than that of an immediate fixed annuity, currently 6.6% for a 65-year-old man.

The big advantage to these deals is that they protect you from precipitous drops in the stock market in the years immediately before you retire, says Steve Vernon, the author of "Money for Life." The trade-off is that the cost of the guarantee will eat into your returns. And although the payout is locked in at retirement, the income base goes down as you withdraw the money, so to produce a higher payout, your returns would have to exceed the amount you withdrew plus the expenses.

If you care more about protecting a chunk of your retirement savings than the impact of expenses, go with this type of annuity, or split the difference by guaranteeing just part of your savings. Don't jump into this complicated product without getting expert advice.

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7. Educate yourself

Depending on your employer, you might get a slim pamphlet explaining your 401k plan and its investment options, or you might get access to everything from investment workshops to one-on-one counseling to online calculators that help you set retirement goals and plan accordingly.

Don't wake up at 66 and wish you'd done your homework when you were 25. Even with automatic 401k features and employer hand-holding, you're responsible for your own future. "This is likely to be the biggest investment account of your life," says Armour. "The correct decisions can make the difference between retiring comfortably and barely getting by."

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