I know several artists sell cards to help market their art. Every card that is mailed, someone is receiving information about your art. But, have you thought about giving your image away?
One idea to reach more potential clients would be to contact different companies to talk to them about giving one of your images to them for their own holiday card lists. Think about companies that you may want to market your art to their clients, someone local, insurance agency, bank, financial group, salons.
Any company that might have potential customers for you, let them use one of your images (with credits of course). They send the cards to their customers, sometimes their best customers. You can reach a whole new audience in your marketing without any cost to you, just the use of one of your images.