After he negotiated a $9 million contract with the Twins that made Kirby Puckett the first $3 million-a-year player in baseball history, agent Ron Shapiro remembers reading headlines asking, “Can salaries possibly go any higher?” Twenty years later, when he convinced the Twins to offer Joe Mauer a deal worth more than 20 times that much, Shapiro was certain of the answer.

“There’s no doubt that Joe left money on the table,” Shapiro said of the eight-year, $184 million contract that Mauer signed in March 2010. “But like Kirby, and like Cal Ripken [also a Shapiro client], he received the tremendous bonus of remaining in the community where he had spent his whole life.”

Had Mauer been a free agent during that winter of 2009-10, coming off the best season of his career and with baseball’s biggest spenders needing help at catching, Shapiro would have sought a 10-year, $300 million contract from the Red Sox or Yankees, “and it’s reasonable to believe the final number would have been much higher than” what Mauer signed for, Shapiro said. “But that’s not what was most important to Joe.”

That left Shapiro to navigate a delicate path with conflicting leverage and a hesitant partner, a fact confirmed when Bill Smith, the Twins general manager at the time, offered $90 million over five years, or $18 million a year.

That Shapiro ultimately convinced Smith and Twins owner Jim Pohlad to more than double their overall package is due in part, the longtime agent says, to the bargaining techniques he reveals in his third how-to-negotiate book, “Perfecting Your Pitch: How to Succeed in Business and in Life by Finding Words That Work.”

Shapiro writes scripts for each negotiating session, which he says allows him to focus and strengthen his argument, anticipate counter­arguments, and avoid off-the-cuff mistakes that weaken your pitch.

“In so many situations in life, you want to make sure you don’t have a conversation, then walk out of the room and say, ‘Why did I say that?’ Being unprepared can do great damage,” Shapiro explained.

Not many people negotiate multimillion dollar contracts, but “Perfecting Your Pitch” offers advice on a huge range of more everyday delicate negotiations, from asking for a raise, to family squabbles, to breaking up with a boyfriend or girlfriend, to talking to children about sex.

“A lot of people try to wing it, but you make critical mistakes that make the process much harder,” Shapiro said. “If you script it, have a devil’s advocate examine the script, and work on delivery, communication — and thus negotiation — is much more likely to be a success.”

Just ask Joe Mauer.