Making the switch from football player to entrepreneur and morning-show host isn't as easy as Michael Strahan makes it look.

In Strahan's book Wake Up Happy, which hit bookshelves this week, the former New York Giant shares many of the lessons he's learned that helped him launch a clothing brand and start a new career after his NFL retirement left him terrified of the future.

"Even though I knew I wanted to retire and left on my own terms, I was scared to death because the next step was uncertain and unknown," he says. 

Here are three lessons Strahan learned that have helped him succeed in his football career and as an entrepreneur and TV host.

1. Don't try to change other people--change yourself. 

Strahan had a contentious relationship with Giants head coach Tom Coughlin from the first day Coughlin joined the team in 2004. "We just flat out did not get along," Strahan says. Strangely enough, it was Coldplay frontman Chris Martin's lyrics--"Am I part of the cure, or am I part of the disease?"--that inspired Strahan to approach Coughlin with a positive attitude regardless off the negativity he received in return. 

The end result was a healthy relationship that helped the Giants win the Super Bowl in 2008. The lesson? "You can't change the way somebody acts," Strahan says. "The only thing you can do is change the way you act towards them."

2. Don't talk yourself out of your goals. 

Wearing a suit six days a week on Live! with Kelly and Michael and Fox NFL Sunday gave Strahan the idea to start his own line of suits and dress shirts, but like most entrepreneurs, he had plenty of skeptics doubting him. "When we have ideas about things we want to pursue and create, we always have people who say 'Oh it's never been done' or 'You can't do that,'" he says. 

Instead of listening to his doubters, Strahan forged ahead and obsessed over every detail of his clothing line, from the width of the lapels to making sure the pricing was affordable. The brand, called Collection by Michael Strahan, launched exclusively  in JCPenney last month. "Don't talk yourself out of what you want," Strahan says. "Other people doubt you enough."

3. Never stop mixing work and play. 

Before replacing TV legend Regis Philbin and landing a job on Live! with Kelly and Michael, Strahan nailed a guest appearance on the show in 2012. How? While Kelly Ripa was interviewing actor Channing Tatum, who was promoting his male stripper film Magic Mike, Strahan ripped off a pair of tearaway suit pants and started an impromptu dancing routine.

"I've been told that that really helped me get the show, because it showed that I'm willing to play and have fun and not take myself too seriously," Strahan says. The lesson? Always look for ways to combine work and play. "We get to a certain age where we think we can't have fun anymore, and we can always have fun," Strahan says.