To complete a successful family reunion you need contacts, support, planning, and lots of answered prayers. In this day and age contacts and getting the word out is easier with social media, but I believe personal contact is still the best. Creating interest in the reunion is the challenge.
This past year  the Braithwaite Family Organization held a successful three day reunion in Manti, Utah. The reunion is held every five years. We sent out seven hundred forty email invitations, advertised on the radio, and set up a facebook page. Three hundred and eighty-five people pre-registered for the reunion. In 2011 five hundred and fifteen pre-registered for that reunion. (For the 2011 reunion I called over 200 family members and personally invited them to the reunion. I believe that to be the reason for the larger turnout.)
The most important thing we do regarding our reunions is attending the temple. One large advantage for us is over five hundred of our email contacts are worthy recommend holders.
We feel that having something for everyone is the second most important thing. Creating good childhood memories plays an important part in keeping Ancestral Family Organizations alive. (I have very fond memories of my own Ancestral Family Reunions as a child.)
We sent out reunion announcements fifteen months in advance so families could schedule other reunions and vacations without conflicting dates. Reminder emails were sent every three months. Fifty invitations were sent for a Committee meeting six months prior to the reunion (32 showed up). We attended the Mount Timpanogos temple, a catered dinner, and then the meeting. The following committees were set up: Advertising, cleanup, displays, fundraiser, games, meals, musical program, pictures, power point presentation, registration, and setup. The more people involved in committees the more it helps to get people enthused about the reunion. We offer catered meals but invite anyone to bring their own food if they prefer.
Day One: We had reunion registration (registration packets included a map of the ancestral homes in Manti, a schedule of events, and tickets for the meals.), unveiled a Braithwaite Memorial in the Manti cemetery (150 attended), and held a catered dinner at the Manti Tabernacle (120 attended). A few families held individual reunions that day. All catered meals were prepaid along with the book orders.
Day Two: We started at the Manti temple. We supplied family names for all who attended. Some brought their own names. Over one thousand ordinances were performed at the temple by family members. Reunion registration, social hour, catered dinner, and power point presentation were held at the Manti Tabernacle. We rented the city pool that night.
Day Three: We started with registration and a skit at the city park. It was written by a family member about our family arriving in Utah. Awards were handed out: the oldest, the youngest, the largest family attending, the person traveling the farthest, etc. A group photo followed by pictures of the descendants of the six siblings was taken. Next was a game with questions about our families’ history. We finished with more games and a catered lunch the rest of the day. A cannon that shot candy over thirty feet in the air was a big hit.
One of the big surprises at the 2011 reunion was how many people came to me and said: I have known this person most of my life and had no idea we were related. The Lord's help was seen over and over in our preparations for the 2011 and 2016 reunions.