As your work improves, add your best works to your portfolio and remove those that haven't endured as well with time. Know how to use these tools to render high-quality size efficient graphics, photos and animations. Adobe Photoshop and Image Ready, and Macromedia Fireworks and Flash are all great tools to be expert in. Don't just look at the writing, look at the artwork as well. Visit stores like Target, pet shops, florists, gift boutiques, sporting good stores, etc.
Most stores have at least a spinner with cards.
Also, read the books out there on card writing. Besides mine, Karen Ann Moore and Molly Wigand have books on the subject. If you're so inclined, take a greeting card writing course. And of course, submit your work. I can't stress that enough.