Well I could, but then the words would be mine and not coming from your heart. This is something you can do, just sit down and put your heart and feelings down on paper. I do this every morning for my man, and I can't imagine ever giving him words from another, as they would not be mine....the only words I want him to have are mine, MINE from my heart and from my soul.
Only you can do so none of us know what he is like.
Sure, I can give you some excellent tips,
1. Become Calm and Get into Mood - If not anything, you atleast need to do this because your writing is greatly affected by your mood.
2. Be original, Don't fake yourself to impress him
2.Do mention following things :
a) Joyful time you both had together
b) Tell him how much you admire him
c) Appreciate everything he has done for you
Do remember : Don't let your letter convey that you are too desperate about him.