To offer someone congratulations, write a message in a cared that fits the recipient and compliments him on his achievement. Use specific details about him to personalize your message. It may be appropriate to include a gift as an addition or an alternative to a card.
Write a draft of your message on scrap paper, or type one on a computer, before writing your message in a card. That way, you can edit your message and write it in the card once it's perfected.
Base your message on your relationship to the recipient. If he enjoys humor, include a joke in the message. You could also include a memory you have of the recipient, such as the first time you met him or a personal moment between you both. If you don't know the recipient well, write a formal message.
Details about the recipient add a personal element to the message. If your recipient is graduating from high school and enrolling in college, you can congratulate him on the college he's planning to attend. Graduation messages don't have to be a specific length, as both short and long messages are appropriate. Graduation is the beginning of a new time in the recipient's life. Include an optimistic message about his future and include any advice you may wish to give.