When you're planning your wedding, keep in mind that your wedding guests may be having a hard time trying to figure out what to wear on your big day. They may have trouble determining the dress code. There are many different types and styles of weddings and each calls for a different standard of dress. You probably wouldn't show up to a beach wedding in your nicest heals and an evening gown and I seriously doubt that you would show up to the most elegant affair in your flip flops.
Don't be afraid to give your guests a heads up as to what the dress code will be. Your guests will feel much more comfortable knowing the dress code beforehand instead of showing up over or under-dressed.
You can let guests know about your dress code through word of mouth, by posting it on your wedding website, or even print it directly on your invitation.