Click here to learn about hosting packages, including a FREE plan. First of all, make your name, age and gender clear. It's not a special thing, but I often receive mails without them. Write where you found your new pal's name.
Some people join in many penpal sites.
Tell your hobbies and interests to your penpal. Even if you don't, your penpal will get to know more about you. If you write your interests are things like music or movies or books, tell them what kind of books you like, who is your favorite movie, books etc. Yours' or 'Sincerely' is OK too. Women sometimes write 'Love' to their female penpals, even in their first mails.