The presentations, seminars, forums and workshops at the Cannes Lions International Festival of Creativity seemed to be near-universally well-attended this year. We at Warc also got in on the act, hosting seminars on effectiveness, best-in-show campaign strategies and the future of planning at the Palais. But perhaps delegates and observers' biggest focus was the Lions themselves: who won, and how to go about winning one next year.

We at Warc focus particularly on the Creative Effectiveness Lions - those campaigns that have won a Lion the previous year, but can also prove business results over time. This year, the Grand Prix went to McCann Melbourne and V/Line, an Australian train operator, for 'Guilt Trips'. (Warc subscribers can read all of this year's entries, as well as an interview with the winner.) In Cannes, I had the chance to sit down with six members of the jury, who shared their opinions on the winner, their top tips for writing a great case study and the one thing that automatically knocked an entrant out of the running.

All videos feature, in alphabetical order: Brandon Cooke (chief marketing officer, mcgarrybowen), Justin Graham (chief strategy officer, M&C Saatchi), David Sable (CEO of Y&R and the jury president), Adam Stagliano (chief international strategy officer, TBWA), John Woodward (worldwide planning director, Publicis) and John Ziegler (CEO for Asia Pacific at DDB).

There was general agreement that the best thing about 'Guilt Trips' was the clear "through line" from insight to execution and results. Coupled with a great creative idea that could be replicated across borders and outside its category, and you have a worthy winner.

In terms of tips for next year, opinions varied. But there was general agreement on one point: clarity and concision in the case study is a key to success. A planner who can write a great case study, in other words, should be especially valuable to agencies.

There were several major pitfalls to this year's entries, according to the jury, with overclaiming on success, the preponderance of hard-to-understand social media results and even some obfuscatory tactics between value and volume share all cited as reasons for knocking a case out of the running.

Food for thought, in other words, for anyone tempted to enter the Creative Effectiveness Lions next year.

So, what next for Cannes? If you want to learn more about this year's Festival, subscribers can read full reports from some of the standout sessions in our Event Reports section. We'll be publishing much more, including a detailed analysis of this year's Creative Effectiveness entries, over the weeks to come.