Invitations are an ingrained part of our culture and yet, for some reason, they often are overlooked in book marketing. This is odd since book marketing is boiled down to inviting other people to read your work.
Keep in mind, an invitation doesn't have to be something printed and mailed. An email can be an invitation if done correctly. Though, I will say that personalized invitations that arrive in the mailbox can make a huge impression.
So where can you use invitations?
Don't put out a blanket post on social media asking if anyone is interested in being part of your blog tour or receiving a book for review. For me, this smells desperate and unless you've got a big name already, is unlikely to net you any serious inquiries. Instead, do your homework and send out personalized invitations (again, this can be an email). Invite only certain people and tell them in the invite why you'd like them to be involved.
It's a party. You need invitations. And if this is a live, in-person event, I'd really spring for the paper invitations here. Go ahead and post something on Facebook and "invite" your friends to the event. But do that in addition to sending out invitations to the people you really want and need to be there.
If you have a mailing list, instead of sending out a general announcement that your book is out, consider sending a more formal invitation. This invite (again, can still be an email) invites your readers to your book and the world you created. It sets the stage for an experience they can have by buying your book, much like buying a concert ticket. You want them to know not only what they get, but also what they'd miss out on by not buying your book.
Signings and other events
If you'll be signing anywhere, you better send out invites to everyone you know within an hour drive. This may sound crazy, but I kid you not that I would be ticked if I found out that someone I knew was signing their own book only an hour away and I missed it. Because I didn't know it was happening. Never underestimate the power that comes along with being an author. Authors may not seem like a huge deal to those of us who are involved in the writing community, but the general public doesn't feel the same way. Authors are still a mysterious force that lives behind the curtain. Use this to your advantage.
Don't forget the press!
And while you're sending out invitations to all these events, don't forget to invite the press. This includes any local radio or TV stations, newspapers, or online reporting groups. And give the library a little love while you're at it. By all means, send them the press release. They'll need it for all the basic information to write up their story. But go ahead and send them an invitation as well. This sets you apart as a professional and tells the media to pay attention.