The five suggestions below will help employees start to nail down important parts of their retirement plan, even if they haven't figured it all out yet:

5. Check Social Security statement.

Most people have two main sources of income during retirement: whatever they've managed to save in retirement accounts—usually 401(k)s these days, as defined benefit plans continue to decline—and Social Security.

And while the latter is becoming increasingly important to retirees as a major—or even sole—source of income during retirement, many people haven't given a thought to just how much that monthly check will be.

To fix that right now, employees can go to the Social Security website and create an account. That will let them view their annual Social Security statement, which by now should be current and include the information from their 2016 tax return.

That statement can provide an estimate of how much to expect per month, in today's dollars, at full retirement age, or how much it will be if filing for benefits early or late. And, based on actual earnings history, it can also offer information on eligibility for disability and survivor's benefits, Medicare and more.

4. Zero in on the grand total needed to retire.

Many workers have no idea at all how much they'll actually need to retire. And that can make it tough to save, because if you don't have a target in mind, how will you know when you've hit it—or even gotten close?

Now is the time to figure out the magic number. One way to start is by multiplying current income by 80 percent (0.8). (Most experts say that people need an income equal to 70–80 percent of their salary after retirement; calculating using 80 percent is staying on the safe side.)

Next, take that Social Security monthly benefit figure and multiply it by 12—then subtract the result from the income need.

Next, multiply the remainder by 25 to come up with the amount needed, in today's dollars (based on the 4 percent rule, which says you can withdraw 4 percent of the total each year during retirement).

And finally, adjust for inflation by multiplying by 1.03 (the approximate historic average inflation rate) for each year between now and retirement. This can be done exponentially: for example, those planning to retire in 10 years can find the inflation factor by raising 1.03 to the 10^th power.

3. Increase retirement contributions.

This could be a New Year's resolution anyway, especially for those behind in saving for retirement. And the sooner it's done, the better—compounding interest is everyone's best friend.

While employees may be accustomed to contributing the minimum—maybe 3 percent—or even just the maximum to receive the whole employer matching fund contribution (maybe 5 percent?), that's far from enough.

These days people should be socking away at least 10 percent, or even more — although they don't have to jump straight to that level. But they need to get started boosting those contributions.

To take advantage of any potential tax benefits for 2017 of higher contributions, employees need to know that as a rule, 401(k) and similar employer-sponsored plan contributions must be made before the end of the calendar year—so no procrastinating.

For IRAs, they have a little more time, since 2017 IRA contributions can be made until the April 2018 tax deadline. But that doesn't mean they should stall on this either—lest they forget.

2. Rebalance portfolios.

Lots of folks don't do this either, sometimes for years, sometimes ever. Employees need to look at their retirement portfolio and make sure it's still appropriate for their risk tolerance—and while they're at it, lock in any gains and cut any losses.

The Fool gives an example of why rebalancing is needed. If five years ago, a retirement saver determined the ideal asset allocation is 75 percent stocks and 25 percent bonds, and then reviews holdings now, in that time, the S&P 500's total return has been 103 percent, while the Vanguard Total Bond Market ETF has returned just 10.6 percent. As a result, the portfolio would now be composed of 85 percent stocks and 15 percent bonds, excluding new contributions.

So now there's too high a concentration of stocks in the portfolio, so it's time to change that and keep asset allocation in line with the retirement saver's goals.

1. Check investment fees.

The fees charged on the investments in a 401(k) plan can kill returns faster than many might think. In fact, lots of the funds in 401(k) plans have fees that are way higher than other funds charge for the same basic type of investment, with the same objectives.

Employees need to make sure to review the charges on all the investments in a retirement portfolio, and compare them with other available options. Called "expense ratios" in the literature for retirement plan or mutual funds, they are the total fees for these investments, expressed as a percentage of the assets per year.

Again, the Fool offers examples: A large-cap stock fund with a 1 percent expense ratio could be swapped out for another large-cap stock fund offered by the plan that has just a 0.6 percent expense ratio.

And while that may not sound like much, remember compounding? In this case it's not a friend, as the Fool points out. If one invests $10,000 in a stock mutual fund that matches the S&P 500's historic returns, there'll be $115,582 after 30 years if the fund's expense ratio is 1 percent. But if instead the expense ratio is 0.6 percent, the total will be $129,073—almost $13,500 more.