Get together some things you can put in the card as a collage. (ex: fun note cards, sticky notes, colored tape, candy wrappers..)
Fold a piece of construction paper into a card shape. Cut a design into one of the sides for decoration.
Stick any kind of material on the cover, but don't add too much and make it fairly flat. Only do this on the outside covers of the card and keep it orderly. This makes your card customized.
Lastly, on the inside of your card, write a message or just simply, "Happy Father's Day" and sign your name.