If possible pick out a theme and start preliminary planning 6 weeks ahead of the party date. Send the invitations out 3-4 weeks early. Phone them if they don’t RSVP (it’s amazing how many people don’t!) Having your guest list ahead of time allows you to adjust for any shortfalls.
Invitations can take many different forms with both the invitation style and method of delivery. Use your imagination for fun ways to invite your guests.