Once you pick the date you want for your wedding, get that date out there to your friends and family.
Start with a "mass email" to get the word spreading. This will also give you a better idea of people that already know they won't be able to come. For us, we spoke with each set of parents, siblings and our closest friends first, and once they all confirmed that there were no conflicts, then we contacted everyone else.
The email is a good idea because it will buy you some time. It's also a good time to ask people to send you their addresses so you can get your address book up to date and organized. If you don't already keep your addresses digitally somewhere, I highly recommend using this time to do so. It will save you a ton of time down the road when preparing to print save-the-dates, invitations and even thank you cards.
I asked a designer friend at work if she'd help me design our wedding stationary. Once we booked our venue, we knew our ceremony was going to be under a big pepper tree. So we thought it would be cute to design a tree for the Save-The-Date and have our names nestled below.
Kevin and I are huge Jack Johnson fans! In fact, we often say that we fell in love to his music. So, we found a set of lyrics from his song "Better Together" and with one slight word change, we had the perfect verbiage for our Save-The-Date.
The Save-The-Date should set the tone (and theme if any) for your wedding. You want it to be personal and represent who you are as a couple as well as get your guests excited about what's to come.
We worked on getting our Wedding Wire website up and running before we sent out the save the dates and included our site address on them. This gave our guests a place to go and start getting more familiar with our story, as well as assist the early birds in booking their travel. For some people, doing all of this prior to the save-the-dates going out may be too much, but at minimum I'd recommend taking the time to build a wedding website by the time the invitations get mailed. It will save a ton of time by answering guest's questions for you!
So, pick something that represents you and your wedding. It doesn't have to be anything fancy, just something special to you.