The decades-old stereotypes of gaming as an environment for antisocial teenage boys and young men living in their parents' basements is vanishing. More than half of Americans, 59%, play video games and the average player is 31 years old, according to 2014 research by the Entertainment Software Association. To reach this coveted affluent millennial audience, more nonendemic brands like phone providers, food companies and consumer packaged goods, are looking to tap the now-mainstream gaming space.

Here are five tips for connecting with gamers.

Don't just slap on a logo

Gaming may be the Wild West for marketers, but simply showing up at an event won't earn points with players. Brands that really want to connect with consumers need to show they understand them.

When Nestlé sought to leverage this year's PAX East convention, the company parked a food truck outside the Boston venue and gave away more than 3,000 Hot Pockets to attendees waiting in line during the three-day event. The effort built buzz for the brand -- Hot Pockets gained nearly 2,000 Twitter followers and nearly 1,300 YouTube subscribers as fans shared videos and pictures of their warm sandwiches during the cold March weekend.

"It worked out really well because they came with a very authentic plan," said Nathan Lindberg, VP-global sales at Curse, a gaming network that worked with Nestlé on the push. "Anybody can buy a banner ad."

Publishers like Riot Games, which produces the popular League of Legends game, are also very selective about the brands they work with. "Our audience is very smart and the partners struggle to understand how to activate in this industry," said Dustin Beck, VP of e-sports at Riot Games. "It's not going to be a simple media buy."

The developer works with Coca-Cola, which made a calculated bet on the gaming realm last year by sponsoring a semiprofessional League of Legends league. The beverage brand saw a gap in the game's league structure, which was only for professionals, and the Challenger Series gave gamers an opportunity to mature into the professional arena. Coca-Cola also matured in the space: It is now a major sponsor of League of Legends' professional league.

Look inside and outside your ranks for gaming talent

More and more brands, like HTC, which sponsors three U.S. e-sports teams, are looking to gamers within their organizations to step up and help navigate the complex gaming landscape. HTC's e-sports project manager Walter Wang is a longtime gamer who helped introduce the company to the gaming space, along with a small group of fellow gamers who run the brand's e-sports initiatives with support from a global team.

"It did take a little bit of coaxing to tell upper management that e-sports was becoming really big," said Mr. Wang. "Happily, I convinced them. … The demographic is also perfect for HTC because they're all tech-savvy millennials."

Coca-Cola also hired a global head of gaming, Matt Wolf, to lead the company's e-sports efforts.

Be choosy and establish boundaries

There are thousands of games for brands to tap into, from PC, console and mobile games to role-playing games and multiplayer online battlefields. Brands need to be as choosy about the games they associate their brands with as they are with TV shows and films.

"Understanding the gaming environment and knowing if your brand is willing to be associated with an M-rated game, those conversations are very key," said Andy Swanson, VP of e-sports and events at the gaming platform Twitch.

When Geico broke into e-sports this summer by sponsoring a Hearthstone tournament, the insurer was very selective, according to Deric Ortiz, a gaming consultant who works with Geico. A dark, violent game would have sent the wrong message for a company that stands for safety. Blizzard's Hearthstone digital card game was a safe bet because it's fun and kid-friendly, he said.

Keep an eye on message boards

Gamers are passionate and have strong online communities. They might share ideas that marketers wouldn't think of. For example, online fans have called on Coca-Cola to make a Coke bearskin, or player look, during the holidays for League of Legends character Volibear, who resembles a polar bear. (The brand hasn't fulfilled the request yet.)

Throw out the traditional sports-marketing playbook

Professional gaming and traditional sports are similar in terms of their league, team and player structures, but their audiences are incredibly different. Sports marketers entering the gaming space should take what they know about traditional sports and build a new e-sports strategy from the ground up.

"[Brands] can bring a ton of cool activations they've done in traditional sports," said Mr. Beck at Riot Games. "But this is a new audience. ... It's not rinse-and-repeating."