The numbers are staggering.

Over 22,000 industry influencers and business professionals attended this year’s MWC19 in Los Angeles October 22-24, where they explored intelligent connectivity, the combination of high-speed 5G networks, the Internet of Things (IoT), artificial intelligence (AI) and big data. In conjunction with this conference, YoMo, a gathering of more than 15,000 students and 2,500 educators, showcased science and technology.

When meetings of this magnitude take over a city, so do ancillary events—gatherings held in conjunction with a citywide that are not officially part of the convention.

During MWC19, ancillary events were held all over the city. “We are the beating heart and catalyst and want others to piggyback off what we are doing,” explains Jack Davidson, Americas engagement manager, GSM Association, the trade body that represents the interests of mobile network operators worldwide and the organizer of MWC.

“Attendees get fatigued going to a convention center for three days. Outside venues can capitalize on that,” says Davidson. During E3, the world’s premier event for computer and video games and related products, approximately 66,000 people packed the Los Angeles Convention Center in June for this three-day event. Although they may not exhibit at the main event, some tech companies set up shop in places like Convene at 777 South Figueroa Street, a short walk from the convention center, and host investor meetings. It was the ideal venue to meet in while major players in the video game industry were in town.

We asked Davidson what the secrets are to planning a successful ancillary event. Here are a few of his top tips.

Create a checklist. An extensive checklist will ensure nothing gets missed. Be sure it is detailed and includes a timeline.

Assemble the right team. Successful leaders know they are only as good as their team. GSM Association has 50 on its event planning team, and they are the best there is, says Davidson.

Set goals. What are you trying to achieve with the ancillary event? Identify its purpose. It’s important to market your event, but you can’t do that effectively until you fully understand what your goals are.

Where will you host it? The meeting space sets the tone for the gathering. Is your meeting an informal one? Choose a small room and set the chairs up in a circle. Is it more formal? A conference room will probably work best. Will there be virtual attendees? Make sure there is on-site video conferencing equipment.

Don’t be too broad. “Don’t spread yourself too thin,” recommends Davidson. “Stick to what you are good at and do that well.”

Plan well in advance. Most ancillary events are held during citywides, and space will be lacking, so book early.

Check, double check, and check again. Triple-check everything. Confirm everything in advance, and always have a backup plan.

Details, details, and details. Every detail matters when planning an ancillary event. Many meeting professionals say they picture themselves as an attendee and ask if everything is easy, obvious, appealing, enjoyable, and surpasses their expectations.

Prepare for unexpected. Changes happen. People are unpredictable. Last-minute requests will occur. Someone will show up that you didn’t plan on showing up. Illness, travel issues, canceled flights are a reality. Have a plan B, C, D in place.