One of the first clients I found right as I left art school in the early 1990's was a greeting card company called Prudent Publishing, whom I still work with from time to time. The process in working with a greeting card company involves working up several comps, which then go into a review meeting. Typically, Prudent Publishing would have some ideas in mind when they'd ask me to generate some comps. So I would quickly paint them up and wait for the review. Sometimes the comps would be approved, and I'd be asked to work one or two of them into fully rendered illustrations. Here are several Christmas/Winter themed comps from several years ago (copyright Prudent Publishing Co.):
Santa! This one never made it to a card, but the comp was really fun to paint!
and below are a few cards that I illustrated: