For an elegant reception cocktail party, cook some hors d’oeuvres and appetizers and purchase some wines and liquors for your guests’ enjoyment. Define a dress code in the invitations and either obtain the services of a DJ or pay your teenager to play music man for the night.
Clear out a space for dancing and set up some chairs / sofas for lounging and conversation. This fancy soiree will be the topic of conversation for months to come.
Be sure to set aside a special place for gifts to be given to the guest of honor. Or, if you know of a particular “larger” or more expensive item the birthday celebrant desires, collect money from the guests as a down payment!