Your clients just won the lottery. Now what?

For Mavis Wanczyk, winner of the $758 million Powerball jackpot, investing her new cash will be the easy part. Keeping it from taxes, shysters and her own human nature will be the hard part. Ms. Wanczyk's after-tax winnings amount to $336 million, which is still a hefty chunk of change.

According to Fortune magazine, you'd be able to buy a Boeing 747 with gold trim from the Sultan of Brunei and still have $116 million left over for luggage. But let's assume Ms. Wanczyk forgoes the gold-plated 747 and settles in with a planner. What is the first challenge she would face? Finding an adviser she can trust, said Jill Schlesinger, senior ambassador with the Certified Financial Planner Board of Standards. She once had clients who won $80 million in the lottery. The couple filled out a routine intake form, noting that he was a teacher and she was a state employee, and that they wanted to make sure that they were on the right track for retirement and their children's education. "I said, 'You don't need me now, but I can create a plan for a few hundred bucks'" Ms. Schlesinger. "Then the wife said, 'By the way, I won $25 million in the lottery. I nearly fell off my chair.'" The couple wanted to see if they could talk to a planner without immediately getting a sales pitch.

Her advice to planners dealing with people who have clients with big windfalls: Assemble a team, starting with a fiduciary adviser and including at least an estate attorney and a high-powered accountant. Come up with a plan for dealing with the inevitable requests for donations for everything from soccer fields to angel investing in Broadway shows.

As for investing: Prefund all the basic needs, such as retirement and education, and do so as conservatively as possible. With such large amounts of money, there's no need to take undue risk. Think of it this way: With $336 million, a 2% after-tax return would generate $6.7 million a year without touching principal. Taxes are a major part of the investment equation. Massachusetts has a flat state tax rate of 5.15%, so add 39.60% in federal taxes and she's looking at a 46.51% effective tax rate. A long-term Massachusetts general obligation bond maturing in September 2036 currently yields 3.4%, which would give Ms. Wanczyk a taxable equivalent yield of about 6.5%.

Tim McIntosh, chief investment officer for PBG Asset Management, said that education is particularly important for lottery winners and others who have come into a sudden windfall: There's a big difference between someone who rolled up a $6 million bankroll over her lifetime and someone who just gets $6 million handed to her. And don't rush, Ms. Schlesinger said. "Don't invest a dime until you have a strategy." Because she was nervous about hitting limits of Federal Deposit Insurance Corp. limits with her clients, she parked their money in Treasury bills until they had come up with a financial plan and an investment plan. One other important part of that plan: Make sure they have some money to spend on what they want. "Have a slush fund so they can do something fun. They want one expensive car? Fine." Just put a limit on it.