You got the job--now what? How to maintain a high performance level in a new job.

Within six months of attorney Pamela T. Miller signing on as vice president of market strategy and development for Medco Health Solutions Inc., she made good on her promise to open a new market and deliver a new client. "I knew that, not only was I ready for the big leagues," she says, "but I had a very good idea of what I needed to do to show that I was worth what it took to bring me [to Medco]."

Unfortunately, many executives aren't as successful as Miller. A study by the Center for Creative Leadership shows that 40% of executives in new management roles flame out within their first 18 months on the job. That means you're on the hot seat from the minute you move into your new office. Taking a page from presidential politics, experts say the first 100 days are critical for success. "It's long enough, in whatever field, for an impression to be made and a tone to be set," says James M. Citrin, coauthor with Thomas J. Neff of You're in Charge--Now What? The 8 Point Plan (Crown Business; $35.00). Adds George Bradt, managing director and CEO of PrimeGenesis, a Stamford, Connecticut-based consulting firm, "During your first 100 days, you're under the microscope. So what you do is magnified."

Whether you got a promotion you lobbied for or you were courted to a new post, it's critical to have a plan before you get a plum assignment.

Here are some tips to help ensure your success:

Know what you're getting into. In addition to learning an industry and company profile, investigate a company's specific situation and status. "Have [an understanding] of how the company's perceived before you're inundated with information from inside the company about how it thinks it is perceived," says Kenneth Powell, senior vice president of Right Management Consultants in New York City. Gather information from people externally--suppliers, customers, consultants, or others who have done work for the company--so you know if you'll be steering a successful firm or helping to reorganize a company in need of a turnaround.

Plan your first 100 days. Write out a plan for your first three to four months in the new position. Decide how you'll synchronize your expectations with the company's, shape your agenda, and manage your boss. Citrin, head of the global technology, communications, and media practice at Spencer Stuart, a global executive search firm, says one of the most common mistakes people in new positions make is promising too much and not delivering. CEOs shouldn't see themselves as company saviors, he explains, but should work through their teams to produce results.

Study before you start. Miller used the month before she started working at Medco to pore over dozens of documents--the company's annual report, public financial statements, and Securities and Exchange Commission filings. She also listened in on an analyst call and sat in on meetings. "It's critical to get information that you may not be able to get once you have formally assumed your role," says Powell, explaining that people tend to be freer with information before executives become official.

Open lines of communication. Be a good listener to not only company stakeholders and key executives but constituents as well, offers Bradt. Ask questions so you can align expectations to produce results. Asking different people the same questions often produces a useful pattern that you can act on, says Powell. For instance, you might ask, "What would you change in the company if you could?" or "What do you expect of me as a leader?"

Get your team in place. Do this as soon as possible. This is a key driver of success or failure, says Bradt. A high percentage of executives fail because they are not able to build a high-performing team fast enough to deliver results within an expected time frame, he explains.

Stand and deliver. Generate some early wins. Make a positive mark on something important to your boss or to the people important to your boss. "Make it something dramatic, something achievable, something that is a model for others and that enhances your standing," says Bradt.