Should I include the dress code on the invitations and how?

If it’s important to you that your guests are appropriately dressed for your event, than it is probably a good idea to specify just to be safe. You can either write something like “Formal” or “Black Tie” if you want guests to dress up. On the other hand, if you’re having a backyard BBQ type wedding and don’t want guests arriving in long evening gowns, you can also write “Casual dress”.