Whatever the greetings you write, as long as all words were from the heart and soul. Unfortunately, when sending a letter it is hardly possible to feel all those emotions that arise in personal communication. But you can always make sure that the letter will remain in memory for a long time, and it will want to read again.
Try as much as possible to write kind words (but only if they are relevant). Even if you are very close with the person, it would still be nice any said in his address a good word.
Wish you many things: health, love, good friends, money, etc. Then there is a standard set of phrases that I write more often. Of course, it would be nice to hear, but because such a greeting is not something special, it will soon be forgotten. But on the other hand, if you remembered the Day of birth and sent a letter of congratulations, then it is good.
If the birthday boy with a sense of humor, always a bit of a joke. Try inserting a humorous phrase (but not just jokes, and those statements that fit the meaning to your greeting).
If you find it difficult to come up with something yourself, try to find on the Internet appropriate greetings in verse and in prose. Don't write a lot of poems in a single message, even the most original. They just become boring to read.
In the letter, be it electronic or paper, you can always insert an interesting picture. Add a holiday to your message with color and bright image, which will be drawn balls, firecrackers, words of congratulations. You can also get creative and invent something of their own.
In the letter it is possible to combine a bit of everything: nice words, cheerful verse and a beautiful image. The main thing is to show a little imagination and write from the heart. After all, only sincere words remembered for a long time.