Greeting Cards

I’m considering writing some greeting cards as a way to hone my writing skills and to make a little (emphasis on little) extra cash. 

So I was wondering what your thoughts are on greeting cards.  What do you look for in a card? What struggles have you discovered in trying to find just the right one to communicate your thoughts?  What do you wish greeting cards would say?

Any thoughts would be welcomed as I think through ideas for writing greeting cards.  I’m a proud supporter of cards, buying and sending many cards on many different occasions.  I know what I look for but would love to hear from others.

Melissa