Don’t make it harder than it has to be. Here are suggestions for your not-to-do list.

Normally this column likes to accentuate the positive, focusing on the best ways to prepare for a happy retirement in the paradise of your choosing. Of course, there are also some things you don’t want to do if you can possibly avoid them. So this month, five common missteps that can sabotage even the best-laid plans.

Not running the numbers

Anybody over the age of, say, 40 should have at least a rough notion of how much money he or she will need for retirement. That’s just as true for people who swear they’ll never retire as for those who are already collecting travel brochures.

Coming up with a workable figure is pretty simple: Estimate how much you’ll be spending once you retire, using your current expenses as a baseline, then compare that with your likely sources of income, such as Social Security and any pensions. If there’s a gap—and there usually is—that’s how much your other investments will have to supply.

The common wisdom in financial-planning land is that you can withdraw about 4 percent of your portfolio each year, adjusted for inflation, with little risk of going broke during your lifetime. So if you need your investments to contribute $10,000 a year, for example, you’ll have to accumulate at least $250,000. A specific goal like that not only focuses the mind but can also save you some needless anxiety if it turns out you’re already on track.

Having only one plan

You might want to retire early, late, or not at all, but fate (or your employer) could have other ideas. And even if you retire right on schedule, the economy, stock market, or any number of other forces beyond your control might disrupt your plans. So it’s smart to have at least a Plan B and possibly a C, D, and so on down the alphabet.

Steve Vernon, an actuary and president of Rest-of-Life Communications in Oxnard, Calif. suggests thinking through some what-ifs, not unlike the stress tests used to judge the soundness of banks. What if the stock market melts down during your retirement? (If you’re retired for decades, that’s a real possibility.) What if inflation roars back? What if you live to 100? What if all of the above happen?

Passing up opportunities to save

Our own surveys have found that if there’s one widely shared regret among retirees, it’s not saving enough or starting early enough. None of us can go back in time and fix that, of course, but we can make sure that we aren’t making the same mistake now. For example, each year you can put up to a certain maximum amount in a 401(k) plan, if your employer offers one. Currently the limit is $22,000 for anybody 50 or older and $16,500 for everybody else. If you can afford to contribute the max and aren’t doing so, that’s an opportunity that won’t come by again.

Same goes for maxing out your contributions to 403(b)s, IRAs, and any other tax-advantaged retirement accounts you might be eligible for. It’s use it or lose it, points out Eric Tyson, co-author with Bob Carlson of Personal Finance for Seniors for Dummies (Wiley, 2010).

Depending on your home equity

It’s too early to feel any nostalgia for the housing bubble, but it did teach us a valuable, if unhappy, lesson. That is, housing prices don’t always rise and can, in fact, go quite dramatically in the opposite direction. So don’t bet your retirement on the house. We usually don’t consider home equity as an asset because there are so many ifs, ands, and buts, says Mari Adam, a certified financial planner in Boca Raton, Fla. Plus, you still need a place to live, and even if you plan to sell a castle and downsize to a condo, you might walk away with less cash than you’d expect, as many retirees have found. Adam points out that the biggest advantage of downsizing can be its impact on expenses.

Ignoring the nonfinancial stuff

By all means get your finances squared away because without that, postwork life can be a struggle. But don’t forget the other essentials, such as maintaining social relationships and having useful and fun things to do. As Tyson points out, often the people who have done the best job of saving for retirement are the ones who have the toughest time spending that money and enjoying themselves. If that describes you (and I fear it does me), plan now to mend your frugal ways!