I've got a friend named Kelly McNamara who is a U2 super-fan. She was 14 when she saw the band for the first time–April 3, 1985, at the Nassau Coliseum on Long Island. Since then, she's caught them more than 100 times.

Kelly is a senior executive in the fashion industry, a loyal friend, and a very fun person to hang out with. She's also part of a core of really devoted U2 fans–a few hundred or maybe even a thousand people–who follow the band on tour, going to show after show. Among the group are doctors, lawyers, students and others from around the world. Some of them travel thousands of miles, and wind up waiting outside or arenas for hours so they can grab the best general admission (GA) spots at each concert.

“Doing GA requires a special brand of stamina," Kelly told me, but touring is worth it to her. "Hawaii was absolutely one of the most unique, the last show of the Vertigo tour. Barcelona, Rome, California, Vancouver, Montreal, all over the place. The one place I have not seen them, which is a bucket list item for me, is Dublin.”

My friend Kelly, second woman from left, and my wife, third woman from left, in the front row of a U2 concert at Giant Stadium in 2011.

What does it take to attract a fan base like that? You don't have to love U2s music to be impressed by the juggernaut that Paul David Hewson (Bono), David Howell Evans (The Edge), Adam Clayton and Larry Mullen Jr. have built. Here are some of the keys to their success.

1. Work with people you know and trust

It's kinda hard to break into this band's circle now. The four musicians met nearly 40 years ago, when they were students at Mount Temple Comprehensive School in Dublin. (More than that, as Kelly pointed out to me, most of the people they work with on tour have been with them for decades.)

2. Understand the business side

In 1984, U2 renegotiated their record deal to give up cash, but to regain control of their copyrights. More recently, and more controversially, they moved their headquarters to Holland to avoid Irish taxes. They were musicians first, but nobody builds a business without understanding business.

3. Make an emotional connection

U2 is doing eight shows at Madison Square Garden this month. My wife and I went to one show (Kelly, of course, is going to all eight),and during it, Bono briefly explained the meaning behind one of the band's older songs, "I Will Follow." Basically, he said he wrote it as a a suicide note as a teenager, after his mother died. Even if you think it was a bad idea for Apple to to automatically download U2s latest album onto everyone's iPhones last year, it's hard not to have empathy after hearing that story.

4. Take risks to stand out

Thirty years ago, U2 was one of the bands playing in London during the two-continent Live Aid concert for famine relief in Africa. In front of 1.9 billion people, Bono took a risk and jumped off the stage to slow dance with a fan, leaving the rest of the band to play a single song for 14 minutes. Immediately afterward they thought they'd blown it, but the unusual performance was a breakout for them. (Rolling Stone magazine wrote about this last year.)

5. Embrace technology

U2s concerts are elaborate, expensively produced shows, and they often include new technology. On their current tour for example, there's a moment in every show when Bono will pull a fan onstage, give her a smartphone, and ask her to broadcast live during the next song via Meerkat. (Also worth noting: Bono made about $43 million on the Facebook IPO in 2012.)

6. Reinvent over and over

There's an anxious undercurrent in much of U2s work, with the group conscious of their status and simultaneously fearful that they're about to fall sharply. (Very Irish of them actually; something I can say given my last name). So, they have a penchant for reinvention. (This doesn't always work out well for them, of course. Case in point, their 1997 album Pop, which most fans consider a low point in their career.)

7. Admit when you screw up

After Pop, U2 was upfront about their disappointment with their own performance. "We're back, re-applying for the job," Bono said repeatedly during their next tour. "And the job is best band in the world." (Their fans forgave them.)

8. Have a bigger purpose

Besides making music, U2s focus has been on much larger causes–from their work with Nelson Mandela and anti-apartheid efforts in South Africa in the 1980s to more recent work on AIDS and African debt relief. Granted, they take some hits for that kind of social consciousness–it can sometimes smack of sanctimony. Still, their fans seem to appreciate it, especially when they're shelling out a few hundred dollars for a ticket or $40 for a concert t-shirt.