The very first lesson to learn is the Rule of 70: Experts in retirement planning say that you'll need to replace at least 70 percent of your final pre-retirement income to maintain your standard of living. So now, while there's still time to adjust, start looking at how you're coming along in adding money to the post-retirement kitty -- from Social Security, pensions and savings accounts.

Can you depend on Social Security?
Assuming that Social Security remains solvent, people age 40 or younger can expect it to replace roughly 25 percent of their current income, says Mari Lynn Cheatham, a certified financial planner with the Georgia Society of the Institute of Certified Planners in Atlanta.

The amount will vary -- Social Security pays more to high-wage earners than low-wage earners. You can obtain a snapshot of where you stand now by requesting a Personal Earnings and Benefit Estimate Statement from the Social Security Administration's Web site. The document estimates your future Social Security benefits and tells you how to qualify for those benefits.

Save with 401(k)s, IRAs
The second part of your retirement income will be savings. Now is the time to maximize contributions to your retirement accounts -- either a company 401(k) plan or your own Individual Retirement Account. The beauty of these instruments is that the interest they earn accumulates on a tax-deferred basis until the funds are withdrawn.

The 401(k) plans have become wildly popular for good reasons: Contributions reduce an earner's taxable income, the plans are usually funded via painless and automatic payroll deductions, and companies often match a portion of their employees' contributions.

IRAs offer the same tax-deferral advantages to people who do not have a company pension plan. An individual may contribute up to $3,000 per year, with the earnings tax-deferred until withdrawals begin at age 59 1/2 or later. Anyone can open an IRA, but people who are not eligible for a pension are allowed to deduct their contributions from their taxable income. Others make contributions to an IRA on a non-deductible basis.

Once you start contributing, don't be tempted into spending. Retirement accounts work only if they remain intact. If you do need the money, consider the tax penalties. First, you must pay income taxes on the amount you've saved. Then, if you are under age 59 1/2, you're assessed an additional 10 percent penalty for early withdrawal.

At the very least, you can set up your own automatic savings plan. Ask your company's human resources department to arrange to have a reasonable amount of money deducted from each paycheck and deposit it into a savings account or money market account. True, these items have low interest rates but regular contributions of, say, $50 twice a month for 25 years equals $30,000 by the time retirement nears. And whenever you receive a bonus, tax refund or other windfall, consider putting 50 percent of it into savings.

Learn pension plan details
If your company has a pension plan, it's time to find out the details.

In traditional pension plans, payments are typically calculated by multiplying the years of service by a percentage of pay earned in the last few years of work. This formula favors employees who stick with a company for a long time -- when pay is much higher in their latter years -- vs. employees who don't stay as long.

Pension plans vary widely, but the calculations usually share the same elements: The final year's salary, years of service and the "retirement fraction." For example, if a person worked 15 years at a company, ending with a $40,000 salary, and the retirement fraction was 2 percent per year, a typical formula would multiply the 15 by .02 by $40,000 -- giving the employee $12,000 a year, or $1,000 a month, at age 65.

A common variation on the formula makes the final years of work even more valuable -- and severely punishes workers who stay only a few years. Using the example above, the first 10 years might have a retirement fraction of only 1.5 percent, the final 10 years 2.5 percent.

A company's vesting rules can also present a pension problem for young people whose careers have taken off. Switch jobs too often and you'll get no pension at all. Companies commonly require workers to stay on board for a set number of years before any retirement vesting begins. If that rule says five years, and you quit after four years and 364 days, your pension is zero.

So know the vesting rules at your firm and look before you job-hop. If you're in an occupation in which frequent job switches are common, you had better be paid well enough to have substantial savings to carry you into retirement -- because there won't be any pension money to help.

Pension plans commonly allow early retirement -- for a price. If you retire at age 60 instead of 65, many employers will cut your benefits by a third, and by half if you depart at age 55.

Don't forget your insurance needs
People with families should also consider their insurance needs. The rule of thumb is that a full-time worker with children should be insured for at least seven years of net, after-tax income, says Randall Guttery, assistant professor of finance at the University of North Texas.

But as with most rules of thumb, there are plenty of exceptions depending on your age, the ages of your beneficiaries and your net worth.

You might also want to consider long-term disability insurance, which replaces your salary or wages if you are disabled before retirement and can't work. Without such insurance and without a job, you'll have trouble saving anything for retirement. Experts say that you're much more likely to suffer a disability than die before your retirement years.

Keep spending in check
Even good faith efforts to save can be thwarted by out-of-control spending. But the key is to build a realistic spending plan for day-to-day expenses and still tuck some money away for long-term goals such as a college education for the kids and retirement. This is not the time to rack up more debt. Keep credit card bills to minimum. Adopt a pay-as-you-go strategy whenever possible.

Too often, people spend more than they earn and end up reaching for credit cards to make up the difference. It's easy for things to get out of hand, says Meg Green, a certified financial planner in Miami. "That's when you have to think about the future, about kids' college, about the house, about the business."

Hand-in-hand with curbing spending is setting up a realistic budget. At this age, if you wait 10 or 15 years before considering how much money you'll need for retirement, you run the risk of not saving enough. If we have a 3 percent inflation rate for each of the next 25 years, today's $100 trip to the supermarket will cost $209.

Avoid being buried in house debt
Finally, this is the age when most people are calf-deep in paying off their mortgage. Experts say it becomes a bit easier to make payments and set money aside for retirement.

Still, most retirees these days are living longer -- and showing a distinct unwillingness to trade down to skimpy retirement homes and the occasional shuffleboard game. Because it takes more savings now to support a big house and an active lifestyle later, consumers have to be extra careful not to overextend themselves when it comes to housing.

That may mean keeping the mortgage manageable so some money can keep flowing toward retirement accounts.

Lucy Lazarony, Michael D. Larson and Holden Lewis also contributed to this story.