Send your birthday invitations. Once your venue and date are set, send out your birthday party invitations to your guest list. Budget. Avoid spending too much money by having a budget set before starting your birthday party planning. Planning the Details: 3 weeks before the party With just weeks to plan for everything, it’s time to decide on the menu, decorations, and entertainment or games. Food – a buffet is the most popular and easiest method of serving food, especially if you’re having the party in a restaurant or at home. It’s relatively less expensive than having an ala carte menu. Serve snacks for guests to nibble on while waiting for dinner to be served.