Be sure to have a handy water or concession station nearby. Your guests will not be under the comfort of a covered gazebo. You might also consider having a few parasols or umbrellas available for those who have not brought one. ?
Gazebos and pergolas lend versatility for decorating. You could choose to use fabrics and swag around the entrance or from the cupola, floral sprays above the entrance, dangle kissing balls from the top of the structure, suspend lanterns, string balls, ribbons, and even decorate the posts with garlands of ivy or flowers.
When considering decorations for a gazebo or pergola, consider windy conditions and secure your decor appropriately. Additionally, consider visbility. Making your decorations too bold, might inhibit your guest's visibility of the ceremony.