Remember that you’re writing this for humans, not for search engines in particular. Or at least that’s what you should be doing. So it helps to be friendly, confident and clear, showcasing all the communication skills you use when talking to someone face-to-face. Inside the text, it’s usually a good idea to also include some humor, to show your personality in some way: you don’t have to go at-length about your personal life, but a few glimpses into your personal preferences would be nice.