What's the most crucial period of time for a new president? Most Americans would say: "The first 100 days." After all, that's when he's establishing a rapport with Congress, enjoying the traditional "honeymoon" with the media, and rolling out his most important policy prescriptions.

A logical answer. Also a wrong one.

Anyone who's ever worked for a new president will tell you it's actually the transition period between Election Day and Inauguration Day, as well as the campaign itself, that can make or break a new administration. Having a successful presidency can depend on whether the new chief executive has used that time wisely.

But there's no reason for a future President George W. Bush or President Al Gore to learn this lesson the hard way. We've just published a Heritage Foundation book, "The Keys to a Successful Presidency," which should be required reading for any White House adviser interested in getting his boss off to a good start.

Edited by presidential scholar Alvin Felzenberg, the book offers the distilled wisdom of more than three dozen experts, including White House officials dating back to the Kennedy administration. Among their recommendations:

Get started "yesterday." Humility is normally a virtue, but waiting until November to plan your transition is a vice. "Get the infrastructure [in place] before the election, because the day after the election everything is going to hit the fan and resumes are going to start rolling in," says James Pfiffner, a government professor at George Mason University. Because they waited until the last minute, President Clinton's staffers nearly foundered on the rocks of "Nannygate" and other early scandals. President Reagan's team, by contrast, was ready to hit the ground running when Inauguration Day rolled around-and it showed.

Treat journalists with care. Reporters are human beings, too, and they respond negatively when they aren't treated well. Contrast, for example, President Kennedy with President Carter: "Mr. Kennedy … divided his time between Palm Beach, Manhattan, and occasionally Washington," says Harvard University's Richard Neustadt. "The press loved to go to Manhattan, and they loved to go to Palm Beach. But can you imagine how they felt in Plains, Ga., living in Americus for weeks at a time and then having to go play softball with the president?"

Find one message per issue-and stick with it. Keep it clear and concise, says President Reagan's former Deputy Chief of Staff Michael Deaver, and be prepared to repeat it over and over. Such repetition can wear thin, even on great communicators like Ronald Reagan, who once told Deaver he was tired of giving the same education speech at every whistle stop while the White House press corps ignored it. Deaver reminded him that the local media, along with key education people, were following it very closely.

Seek advice before unveiling policy initiatives. New presidents can avoid legislative missteps by heeding the counsel of various experts and congressional leaders. This tip might have helped President Clinton avoid his gays-in-the-military fiasco, according to University of Vermont professor John Burke, who noted that then-Sen. Sam Nunn of Georgia-a fellow Democrat-warned Mr. Clinton before the election that such a proposal would meet with strong resistance.

Lastly, realize that after the election you are no longer a candidate. "It's not enough to give a great speech," says former Kennedy counsel Theodore Sorensen. "You have to have answers … you must exercise much greater caution and provide much greater depth when you speak. Your obligation now is not merely to your party, but to all Americans."

Edwin Feulner is president of The Heritage Foundation (www.heritage.org), a Washington-based public policy research institute.