To write romantic love letters, use special stationery and pens, open with a term of endearment, and write a message from the heart. Stay focused on the sentiment you are expressing, close the letter with another term of endearment or an exclamation of love, and enclose the letter in an envelope with the receiver's name and address written in calligraphy.
Use heavy stock, colored paper or special stationery that shows you took care in writing the letter. Write the text using a nice pen or one with special ink. Open the letter with a salutation such as "My Love," or "My Sweetheart." If you are not partial to a pet name, write something simple using the person's name, such as, "My dearest Amy." The body of the letter is written more like a stream-of-consciousness than an exposition. It tells the person how you feel about her, and what it is about her that you love.
Keep the focus of the letter on the receiver's positive traits. Avoid discussing anything negative or mundane, while being as flowery in your language as is comfortable for your relationship. Finish the letter with a declaration of love before writing a conclusion and adding your signature. Carefully fold the letter to fit in the appropriate envelope. Add the receiver's name and address, and any other desired embellishments to the envelope that do not interfere with the mailing requirements.