Image: Retirement funds © Don Farrall, Photodisc, Getty Images

Ah, for the days when employers worried enough about your old age to set aside and invest money on your behalf, assuring you of a secure -- or at least sustainable -- retirement.

Actually, employers still worry about your old age, but now they mostly use your money, plus the power of inertia, to get you where you need to be. Companies are not only automatically enrolling employees in 401k's -- the pretax accounts that have mostly supplanted pensions -- but they are also choosing employees' investments and boosting contributions on an annual timetable. You can decline to participate, but most people don't, either because they don't get around to it or because they like the results.

The approach seems to be working. Over the past five years, the percentage of employees participating in a 401k or similar defined-contribution plan has held steady at 77%, according to the Transamerica Center for Retirement Studies, despite the bear market of 2007-2009. And account balances have risen, from a median of $74,781 in 2007 for the baby-boom generation to $99,320 in 2012.

If you're like most people, you still need to save harder and longer to accumulate enough for a secure retirement -- say, for an annual income that replaces 75% to 85% of your final pay. And 401k's keep evolving. So, rather than letting your employer make all the decisions, get the retirement you want by following these seven steps:

1. Beef up your contributions

Concerned that employees aren't saving enough for retirement, Congress has authorized employers to automatically enroll workers in the company 401k and peel off 3% of their pay (gradually rising to as much as 6%) for the plan. Now, 56% of plan sponsors use auto-enrollment, up from 44% in 2010, reports the Defined Contribution Institutional Investment Association.

Automatic enrollment helps get procrastinators off the dime, but it can also send a message that a contribution rate in the low single digits is enough to create a comfy nest egg. Rather than be content with a 3% to 6% salary deferral, you should be setting aside at least 10%, up to the annual max ($17,500 for 2013 and, if you are 50 or older, another $5,500 as a catch-up contribution), says John Killoy, of Transamerica Retirement Solutions, which designs retirement plans. "If you reach your 30s and haven't saved a lot, you'll have to look toward 15%. If you're 50 and haven't saved much at all, you're going to have to be much more aggressive than 15%."

In the real world, most participants contribute far less; the median contribution is 7%, according to the Transamerica Center for Retirement Studies. If nothing else, at least contribute enough to get the full company match. "It's company compensation," says Killoy. "You've earned it. By not meeting the match, you're leaving money on the table." Then try to ratchet up your contribution by another percentage point a year.

2. Consider the mix

Companies offer 19 choices, on average, in their 401k's, but the number can go as high as 70 or even 100 -- a selection that can be "overwhelming" to would-be participants, says Killoy. Some companies are cutting back on the fund offerings and adding brokerage windows so investors who want more choices can trade outside the plan.

Whatever the menu, you'll likely see actively managed domestic and international stock funds and bond funds as well as at least one index fund and a money market fund. Most plans also offer a series of target-date funds, which start with mostly stocks and ease into bonds and cash as they get closer to the target date.

The general rule is to load up on stocks while you're young and have time to weather a few market downturns, and move to less-risky investments over the ensuing decades. "If you're in your 20s and have a relatively high risk tolerance, you could be 90% in stocks, with a 10% bond weighting," says Gil Armour, a certified financial planner in San Diego. "Someone who is very close to retirement should have a portfolio of about 50% stocks and 50% bonds."

3. Go with a target-date fund

If you don't designate your own investments, the law lets firms pick one for you. The three kinds of investments they can offer with immunity from liability (that is, you can't sue if you lose money with the company's choice) are: a series of target-date funds, a fund that offers a static blend of stocks and fixed-income investments based on your risk preference, and a managed account, in which investment professionals tailor your portfolio for you. You'll receive a notice of your right to select your investments yourself. The default kicks in if you fail to do so.

Each option offers you a diversified portfolio. But target-date funds have become the investment of choice not only for employers, as a default, but also for experienced investors who like the convenience. "It's a no-brainer type of investment," says Armour. "You can stick with it into and through retirement -- as long as you understand the mix."

That's a major caveat. Target-date funds generally allocate 85% to 90% of their assets to stocks in the early years but vary widely in their stock allocation as they approach the target. For instance, Morningstar reports that funds with a 2015 target date range from 20% in stocks to as much as 78%. Don't find out too late, as many investors did in 2008, that your fund leaves you more exposed than you care to be.

Funds also differ in how they define "target date." Some set the end point at or near your actual retirement; others continue to adjust the allocation for several more decades, keeping the balance more heavily weighted in stocks over a longer period. If you prefer an aggressive approach, pick the fund with an end point that extends past your retirement date. For a more conservative mix, go with one that stops the clock at your retirement or before.

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