-The design should be visually appealing.
-The editorial message refers to the actual words on the
card such as "Happy Birthday."
-The materials are important and will determine whether the design will be easy to reproduce in an easy, consistent and in a cost effective manner.
When developing a card line, it is usually a trial and error process.
You need to experiment with many materials, themes and ideas and it's
usually a good to take time and explore all the possible directions.
Visit card stores, look at what other people are doing, and try to
examine different ways you might manufacture the card. Also think
about mass producing the card and how much the materials will cost you.