Have a clean house/dorm/building.
Have chairs/seating already set up and ready for people to arrive.
Put a candle/air freshener in the bathroom. Also, have a clean hand towel and plenty of toilet paper available.
Put food in serving dishes (i.e. take the chips out of the bag and put them in a bowl), take plastic forks out of the box and put them in a glass, etc.
Have music playing in the background. Make sure the music is not distracting or inappropriate, but just playing quietly in the background. Leave it on but turn it down during the discussion time. The background music helps things feel homier and fills any awkward silence that might occur.
Be ready when people get there (clean, food, chairs, etc.). Have all your stuff (notes, discussion questions, announcements, etc.) good to go before anyone arrives.
Make sure to talk to new people and not just your closest friends. Introduce people and make connections. Encourage your regulars to also connect with new people since you will be welcoming everyone.
Offer your home/dorm for people to cook in (those bringing the food might live in a dorm with no kitchen or not have cooking utensils), offer snack suggestions or recipes if necessary.
Create a fun party atmosphere as best as you can (without the balloons and streamers), just make your space as comfortable and homey as you can.
Remember your Challenge Community gathering does not start when the discussion begins. It starts before people get there through your readiness and preparation, and it does not end until the last person leaves. You know you’re doing well when people don’t want to leave.