All parties start with an invitation. In this day and age we have a lot more options than we used to. You can go digital, paper or over the top with a gift announcing the event. Generally, your invitation sets the tone of your party.
Paper is the traditional way to extend an invitation. Bachelorettesuperstore.com has an entire section dedicated to paper invites. You can go with a customized invitation, an imprinable one or a generic fill in the blank. Along with deciding which type you like you then have to decide naughty or nice, colors and style.