If the only retirement plan your employer offers is a 401(k) account, you've got to sign up and make the most of it.

We can't guarantee that you'll be able to build the nest egg you need for the retirement you want.

The ultimate value of your 401(k) account depends on so many things -- how much you make, how much you save, how long you have before you retire and how well the stock market performs over that time.

But we can guarantee this: Some savings will always be better than no savings.

Our 7 simple rules for a successful 401(k) account can help you do as well as possible by making all the right decisions about your retirement plan.

Rule 1. Choose a Roth 401(k) account if it's available.

The Roth 401(k) is new on the scene. Unlike traditional 401(k)s, your contributions won't be tax deductible.

But when you retire, none of your withdrawals are taxed, including all of the money you'll earn from capital gains (the increased value of your mutual fund holdings), interest and dividends.

Most families don't save that much by deducting 401(k) contributions -- about $350 for a family of four making the national median income of $42,300 a year and contributing $2,400 to a traditional retirement plan.

That advantage is more than offset by avoiding all taxes on your earnings, which will grow to become the majority of the money in your account.

This is a particularly good choice if you're in your 20s and 30s and not making nearly as much as you expect to later in your career.

Your contributions are being taxed at a relatively low rate, and you're earnings will never be taxed, no matter how much your income might grow in the future.

Rule 2. No Roth? Go traditional.

If your company doesn't offer a Roth 401(k) account yet, that's OK. Choose a traditional 401(k).

There's no need to wait. It's important to start saving for retirement now.

The difference: With a traditional 401(k), you pay no taxes on what you save or what you earn from your investments until you begin withdrawing money from your account.

When your company adds the Roth 401(k) to its menu, you can sign up and switch all future contributions to it.

All of your past contributions will remain in the traditional 401(k) and continue growing until retirement.

Rule 3. Start small and gradually increase your contributions.

The major reason employees don't take part in their company's 401(k) plan is a perfectly understandable reluctance to have more money withheld from their paychecks.

So start small by setting aside just 1% of your pay. You'll hardly notice 1%. We promise.

If you're contributing to a Roth 401(k), every dollar you contribute will be a dollar less in your paycheck.

But since traditional 401(k) contributions are not taxed, your take-home pay will only fall 65 to 90 cents for every dollar you put in your retirement account.

Let's say you're making $40,000 a year. Contributing 1% percent of your salary adds $8 a week to your retirement account, but only reduces your paycheck by $7 a week. If you're making $90,000, you'll be saving $17 a week but only see your take-home pay drop by $11.

Once you've started contributing, your next goal should be to qualify for any matching funds your company is willing to put into your retirement account.

Laws governing 401(k) accounts encourage employers to match the first 1% of your savings dollar-for-dollar and then contribute 50 cents for each additional dollar you save up to 6% of your annual earnings.

That's an extra 3.5% you could be earning every year and that you don't want to leave on the table.

Even if your employer stopped making contributions to retirement accounts during the recession, don't use that as an excuse to stop adding money your 401(k).

Gradually set aside more money for your retirement plan by increasing your contribution 1% a month for the next five months. Too fast? How about an extra 1% every six months, or even every year?

The new rules allow you to sign up for automatic increases, so you don't have to call or submit a form each time you want to boost your savings.

Your ultimate goal should be to keep pushing your contributions up a percent at a time until you're saving 10% of your income in your retirement fund.

A growing number of experts say you've got to save at least that much, over a significant number of years, to secure a comfortable retirement, especially if your 401(k) plan and Social Security are going to be your only sources of income.

Rule 4. Choose the right investment.

Another reason employees fail to sign up is that they don't know what to do with their contributions.

Most plans require you to put your retirement savings in a mutual fund -- a type of investment that pools the savings of tens of thousands of people to buy a broad range of stocks, bonds or both.

After the market meltdown of the Great Recession, we can understand why you might want to put your money into something safer -- such as a CD, Treasury bonds or a money market account.

But you have no chance of building the nest egg you'll need for a comfortable retirement by settling for the 2% or 3% those investments typically pay.

You need the historically higher returns provided by the stock market to have any shot at success.

Don't be overwhelmed by the number of mutual funds companies typically ask their employees to pick from.

Here's how to sort through all the choices and find a good mutual fund to start out with:

If your employer offers what's called lifecycle or target funds, choose the one designed for the approximate year you plan to retire.

The professional managers running these funds take greater risks with your money when you're young, buying a mix of stocks and bonds with the most potential to increase in price and boost the value of your 401(k) account. Of course, those kinds of investments are the most likely to tumble if the market falls. But there's plenty of time for the market and your retirement savings to rebound.

As you get older, lifecycle funds adjust their mix of stocks and bonds to take fewer risks and ensure your money is there when you retire. Your account may not grow as fast, but it won't be as susceptible to downturns in the stock market, either.

If your retirement plan doesn't offer a target or lifecycle fund, then invest in a mutual fund that buys shares in all the companies represented in a widely watched measure or index of how the stock market's performing.

Index funds don't buy stocks that managers expect to outperform the overall market. They buy a broad range of companies on the assumption that stocks, as a whole, become more valuable over time.

Historically that's true, even though stocks took a beating during the recession.

If neither of the above options is available, then go for a traditional mutual fund that invests in a broad range of major corporations. The information sheets from your employer may refer to these as "large cap funds," using the financial industry's shorthand for capitalization.

If there's more than one large cap fund to choose from (and there probably will be) pick the one with the best 10-year average return. Yes, 10 years -- after all, you're in this for the long haul.

Rule 5. Don't invest in your own company.

The old adage, "Don't put all your eggs in one basket," definitely applies to your retirement plan.

Many employers will allow you to buy shares in your company as an alternative to investing in mutual funds. They'll also pay matching contributions with company stock.

But you're already dependent on your company for a paycheck and health insurance, so adding its stock your 401(k) plan makes you even more vulnerable.

If your company collapses, you could lose everything: your job, your benefits and your retirement.

Think of the folks at Enron. More than 4,000 employees lost their jobs when the energy-trading company filed for bankruptcy. Many also lost their life savings because they'd filled their retirement accounts with Enron shares.

Learn from their mistakes. Don't use your contributions to buy company stock, and if your employer gives you shares, sell them each time you've accumulated a few thousand dollars worth. Reinvest that money in your mutual funds.

Rule 6. Watch, but don't touch.

You've done it; you've invested in a mutual fund. Way to go. Now let it grow.

It's time to sit back and let the professionals -- your fund manager -- work for you.

Mutual funds are long-term investments that should recover as the economy improves.

In other words: be patient.

Don't fret over the daily ups and downs of the market. Only look at your 401(k) plan and how your mutual funds in it are doing every quarter when you receive the statement.

Revel in the gains, but don't panic over the losses. If it's down, let it be. Every fund goes down and rebounds when you're in it for the long haul.

Rule 7. Don't borrow against your 401(k).

Yes, it's your money. And yes, you can borrow against it.

But no, it's not a good idea.

If you borrow money from your 401(k), that money is no longer working for you and your retirement. And then you've spent that money. And now you have to figure out a way to pay it back within a specified time, usually five years.

That's right: Even though you've essentially borrowed your own money, it must be paid back. Only this time, those aren't pretax contributions (which, by the way, you should still be making). You repay the loan from money in your checking or savings account.

If you don't pay it back, your loan will be considered a premature distribution -- and a premature anything is typically not good.

In the case of your 401(k) account, money withdrawn before you're 59 1/2 incurs a 10% penalty, and you have to pay state and federal income taxes on the amount.

Also, if you change companies, you have to pay back any loans against your 401(k) before you leave your job. If you don't, your loan will automatically be considered a premature distribution.

As we said, borrowing against your 401(k) is not good.

By Darci Smith

Interest.com Contributing Editor

Have a question about your finances? Ask us at editors@interest.com