I feel the most important thing is keeping a conversation going. So I try to have back-and-forth questions.

I'm torn if face-to-face interactions help significantly. Although, if I see someone enough in an unstructured way, I'll either become good friends or want to not see each other again. :)

Facebook is great for keeping in touch in a casual way. Ask questions here and there, comment on their life achievements, etc.

I've noticed that once I got more of my professional network on Facebook, I've been more conscious about posting drama, this-is-how-it-should-be opinions, etc. That's a good thing but man was it hard at the beginning to keep myself from posting rants!!! :D