Finding the perfect birthday card for your son is no small feat. The words printed on the card probably have a nice message, but it's more personal to include a short verse for your son that comes straight from your heart. Don't sit there staring at the card, as the words won't write themselves. Instead, think about your son and what you really want to tell him on his birthday that you might not say very often, if ever.
Consider the type of card you purchased, whether it's heart-felt or funny, if you want the tone of your message to match that of the card. Your message can coincide with the message in the card or be completely different if you want to tickle his sense of humor and add a touching verse. Alternatively, you can expand on the card's message.
Figure out the most important thing you want to say. Look through birthday verses that have already been written if you aren't sure where to start. For example, Love-of-Poems.com and Things-to-Say.com have birthday verses written specifically to a son.
Pick out something meaningful that you want to say, such as trying to express what he means to you, how proud you are of him or what your hopes are for him. Alternatively, concentrate on what he's brought into your life and how lucky you feel to have a son like him.
Write from your heart. Share one of your favorite stories about your son's childhood, comment on how proud you are of where he's at in life now or where he's headed. For example, "You have warmed my heart since the day you were born. I loved watching you play doctor as a child, and seeing you fulfill that lifelong dream has been like my own dream coming true."