In addition to simply saying how one feels, it is also good to include some figurative language putting some imagery with feelings. Some common images that are associated with Valentine's Day include the idea of a lock and key, with the person receiving the card owning the key to the sender's heart. The idea that the recipient makes the sender feel light and airy often inspires comparisons to butterflies, birds, light clouds, feathers and other airy object. The goal is to communicate the depths of one's feelings.
Sincerity is the key to writing a truly great Valentine's Day card. If the relationship is new when Feb. 14 rolls around, then it is not wise to go overboard. However, a simple statement of the other person's meaning sends a powerful message that is likely to stand the test of time.