Send Save the Dates and Set up a wedding website. This should have probably been rule 1 or 2, but well, I didn't do it that way.
Save the dates have become the norm, but when planning an event that requires your guests to travel, it is imperative. Your save the date should at the very least include:
~The date(s) of your event
~The city and state (and/or country for international affairs)
~Your wedding website address
What I also find helpful(and so will your guests):
A summary itinerary: If you're planning multiple events over several days- let everyone know!
Basic travel information: How will most guests arrive? Give info on airports, drive times, car services, etc.
Accommodation information (where you have rooms blocked at). Include Addresses, phone numbers, website, and a little info if its more than just a "hotel"
Here are a couple of our client favorites...