Inspired by a question I recently answered...
I usually message someone if I notice their bio has rock/metal music, or if they have their pets in their profile picture. Or if I love their opinion and want to continue talking about it without having to blow up the Askers notifications.
Most Helpful Guy
I'm usually impressed by them in some way. Humor or Content wise. And very rarely I may contact someone over furthering my understanding in their religion. Honestly I am very bad at it random messaging. media-cache-ec0.pinimg.com/.../...4f98bb495400.jpg like this1
Most Helpful Girl
If they seem fun to talk to based on their opinions and discussions we've had through the replies, I'll message them to discuss those things or just to let them know they're cool. :P1