Save the Date cards can be mailed up to one year, or more, in advance of your wedding and should mention that an invitation will follow.   Make sure that your guest list does not need any thinning as every guest that receives a Save the Date should receive an invitation and vice versa.  

Keep the wording simple.  All you really need are your names, wedding date and the location.  You may opt for a Save the Date that matches your invitations but don’t limit yourself.  There are also many fun designs that just may speak to your lighter side.  Another very popular and highly suggested option is to create Save the Date Magnets.  Many recipients of these magnets are much more likely to post it on their refrigerator, and are much less likely to forget.