Brian Wieser, who joined GroupM as global president of business intelligence in February from his role as senior analyst of Pivotal Research Group, says the trick to getting through Cannes is to start early.

"I have a very different approach to Cannes," Wieser says, who tries to schedule meetings from 7 a.m. to 8 p.m. "I try to skew it early which I think makes it more effective."

For Wieser, Cannes has always been worth it. Even when he had to pay for it "on my own dime," he adds. "It's just ridiculously effective to meet people from around the world."

Wieser also provides a tip on how to measure effectiveness of campaigns, particularly experiential activations that can be hard to track. (Of course, activations from brands including HP, Live Nation, Hulu and Pandora flood the French Riviera.)

"It's very hard to assess," Wieser says, advising brands to review the entirety of campaigns. "If you notice that campaigns have some sort of activation, that’s really customized, really bespoke, really unique, and those campaigns tend to do better, that’s probably a good idea you should be doing more of them," he notes.

He says, assess "the forest" not "the tree."