Writing the perfect greeting card is a gift. Not many people know how to say exactly what they mean, let alone put it in writing. That's why writing a card for your sweetheart's birthday or your anniversary can be so daunting. You've already picked what you think is the perfect card, but that blank space inside is a little intimidating. The vague message of love and companionship is nice, but simply signing your name underneath just doesn't cut it.
That's the first and foremost rule, as well as the only one you really need to go by. Writing sentiments that you don't feel will come across as fake, and using someone else's language will also come through. Use words that you would normally use in everyday life, not flowery, poetic verse (unless you do actually talk like that.) Tell them how much they mean to you and why they're as important to you as they are.
If you're having a hard time finding exactly what it is to say, a list can be really helpful. Make a list of all your favorite qualities of theirs, from the way they smile, to their quirky taste in music. Start off with acknowledging the occasion you're writing the card for, and go into the many reasons why they make your knees weak. Using a few examples off your list not only shows that you pay attention to them, but that you think of them and love them for a variety of reasons.
Don't make the whole message sappy or the whole thing full of jokes, but find the comfortable in-between. Showing that you care for them but at the same time making a joke (maybe even including an inside joke you share,) is a great way to lighten the mood of any card. It also highlights your great sense of humor and playfulness.
Include your favorite memory of you two together or a common bond between you. If you're both into politics, include your predictions in the upcoming elections, or if they love your cat, include a hand-drawn picture of the two of you with the cat—ok, that's a bit wacky, but you get the drift. Anything that personalizes the card and lets them know you know them inside and out is a winner.
A great way to give your card a little extra something is to include your favorite photo of the two of you together. You could either cut it out and paste it into the card or simply leave it inside on its own. Mention the photo in your message, letting them know how much you love this picture, and more likely than not, that picture will end up finding a place into a frame or an important place in their heart. It's a great way of showing just how much thought you put into the card.