A few months ago, I spent several hours on a grounded plane in Denver, waiting for a storm to pass. Eventually, I ran out of conversation with my seatmates, but another group kept going strong--those still wearing name tags from the Aspen Ideas Festival. They were laughing, discussing business, and making plans to meet up in New York in the coming weeks. For them, the storm was just one more fruitful net­working event.

Even as social media sites like LinkedIn and Facebook keep you connected, meeting people in real life remains the most effective way to build a successful business. In 2016, conferences and trade shows are a $13.8 billion industry, one that's growing more than 2 percent annually, according to market researcher IBISWorld (and benefiting many publishers that organize events, including Inc.).

At their best, these events offer a chance to make new contacts, catch up with colleagues, and learn a few new tricks. "As a startup, conferences are crucial to building a network in our industry," says Felicia Schneiderhan, co-founder of 30Seconds­ToFly, a business travel manager.

But conferences can get expensive: Registration fees may be substantial, and there are travel and hotel costs. Also, they take you away from the company you're trying to build. So how to decide which events are worth your time and money?

For Anna Curran, the founder of the DIY publishing company CookbookCreate.com, the most important factor is the guest list. "Are these influencers and people who are on the rise?" Curran asks herself before spending money on events. "Is this a network I can reach out to in the future?"

One of her favorite events is Austin's annual South by Southwest conference. Soon after she launched, Curran approached the festival director and pitched a themed recipe collection crowd­sourced from festival speakers. The result, The Official SXSW 2014 Interactive Cookbook, gave Curran's fledgling company a valuable publicity boost: Contributors included Randi Zuckerberg and Zappos CEO Tony Hsieh, and the book received a flattering write-up in The New York Times.

"With the festival badge, flight, and hotel, it's cost $1,500 to $2,000 every time I've gone," says Curran, a five-time SxSW attendee. Given what that $10,000 expenditure has done for her business, she has seen "absolutely a good return on investment."

Mike Garrison, a serial entrepreneur and partner at Pinpoint Dental Consulting, a practice-management business for dentists, attends events only when he'll know other attendees or exhibitors. "Personal introductions to key people can create relationships," he explains.

That's not always possible, of course. Sometimes the point of attending a conference is to make professional contacts. But proximity doesn't guarantee success, especially if the events are overscheduled. "One big mistake many conference planners make is they overprogram, and don't give attendees enough time to meet one another," says Curran, who advises checking schedules to see if there is ample break time.

And what if you can't afford the price of attending an event or the cost of skipping it? Consider getting close to the action without actually participating. At a recent, very pricey travel-industry event, Schneiderhan checked into the conference hotel--but instead of registering and attending the official sessions, she stationed herself in the hotel lobby and caught attendees on their way in and out. She wasn't the only one doing it: "People made appointments in advance to meet in the lobby," she says. It's not always the best way to accomplish your meeting goals--but it probably beats waiting for a flight delay.