According to Hallmark, a birthday card can open with a simple "Happy Birthday," and then include a warm and friendly expression of good wishes. A birthday card lets someone know that they are being thought about on their special day.
Some birthday cards already have salutations and messages printed on them, but you can expand upon the prewritten sentiments to personalize the card. Hallmark suggests adjusting the tone of the card's salutation and message from familiar to casual or formal based on your relationship with the birthday person. Express love and affection toward a family member, share a fond memory or inside joke with a best friend or simply wish a coworker a successful year.