Masculine or neutral stationary (paper or email background).
A good writing instrument.
Step1
Sit quietly for a few minutes. Picture him in your mind. Think about the way he makes you feel and why.
Step2
On a scrap of paper, jot down a few key words based on your thoughts. You can either formulate sentences out of these words, or simply use the words, alone, to convey what he means to you and why.
Step3
Limit your sentences to 15 words. Limit your letter to four or five sentences, maximum. Three would be ideal. Men have very good imaginations, being the visual creatures they are. They don't need a lot of words to understand what you mean.
Step4
Add a scent. If there is a scent you wear that he knows well, spritz a little in the air and wave your love letter through it. It will carry the smell without being overpowering.
Tips & Warnings
Men are visual animals. Keep your words few.
Add a sketch or photograph to your letter. Or, if you're sending an email, find an image that conveys your feelings and include it at the end of your words.
Be sincere and honest with yourself; it will show in your words.
Lace and frills should probably be avoided. Consider his tastes when choosing stationary or an email background.