One of the hardest things for us people to do on loved one's birthday is to write something in a birthday card. We as people always seek the easy way out, we simply find a nice card, write a few words , sign the card, and give it out. When the person who receives the card, they are thankful, but deep down they would have really liked had been a bit more 'thoughtful'. With that said, I would like to give you a few ideas, of things to write in a birthday card, to make it more personal, and thoughtful.
People always love to remember, they become nostalgic, and cheerful when they remember the good times. One of the best things to write about in a birthday card is something you remembered, that was fun, and memorable that you did in the past with the person whom will receive the card. For example your are writing your girlfriend , or boyfriend. You will want to think of something you two did together that was fun. Say you went together three months ago to a festival, and you two had a blast together. Thus in the content you would write about this day, and be detailed, tell about how you had such a good time , and how you never forget the kiss you two shared at the top of the Ferris Wheel, or how you both laughed when the ice cream fell on your boyfriends shirt. People love details, so be detailed. In the greeting add a few memorable things as such, this is very personal, and very thoughtful. Anyone can think of a good time they had with near anyone, and if your going to give a birthday card, well I'm sure then, it will be given to a person you at least 'like'.
Another idea of happy birthday wishes to add to a birthday card to make it unique, is to add some humor (this doesn't always mean writing a joke). A birthday should be a cheerful, memorable day thus always keep things on a light note. Don't be serious! You can add to the card something about the person that makes you always smile when you think about them, for example you would write, "I think about you every time I drink my coffee, because you have such a cuteness about you when you drink". Another example would be if your boyfriend is a carpenter, you could write "Every time I hear a hammer pounding, I think of you". People love it when you think about them, and they love when they hear personal unique things about themselves.
You don't need to write a short book when writing a birthday card, just a few sentences are enough. Keep the content personal, and lighthearted. These types of birthday cards will always be remembered by the receiver. I still remember a birthday card I received when I was 11 years old. I remember it because of the content, and what was written in it. The card itself I don't remember what was on the cover, but still to this day I remember every word that was writing in that card. So keep it simple, and personal.