The reader should be able to tell you are friendly; just keep it casual and polite.
If you have a sense of humor, laughter almost always works in your favor.
With the anonymous nature of online dating, personalizing your first message is especially important.
Bring up common interests that prove you have read their profile.
Finally, make sure your first message leaves the door open for a response.
You should ask yourself how you would respond if you were receiving the message.
You run marathons but 'movie marathons' is your favorite activity… " A generic greeting, improper grammar, and a shallow pick-up attempt all make this a terrible first message.
Men may also want to consider a rather strange approach that was uncovered by Ok Cupid: This dating website found that men who appeared vulnerable actually received more replies than those appearing too confident, quite the opposite of the real-world dating experience. The thought is that these words create uncertainty, leading to a sense of vulnerability, and ultimately make you seem less threatening.
Many people using online dating websites are shy, which may explain this.
Ok Cupid found that first messages containing the phrase "you mention" were replied to 48% of the time.
Reference something important to both you and the recipient to make your message personal and form a connection.