Here's something for everybody. How to write love letters. Based on book The 50 Greatest Love Letters of All Time by David Lowenherz, he emphasized that "It's honest affection that really counts". So how? Try to:
Use simple prose
Try to be simple. You can try the flowery talk, but just leave it to poetry. Write naturally, like you yourself and simple expression such as, "I've never been as happy since the day I met you" will do better.
Telling him/her that he/she makes you smile is nice, but it doesn't get much. Go to the specific, though little things like: "I love you that every time that you fill the car with the petrol that I need, and that time when you offer yourself to drive on long trips," etc.
Love letters by email are better than nothing. But those inks, stationaries and time requires to say what you really means that make it alive and beautiful.
Hope that can give a little love to all. Bye, have a nice day. :)