"Admit when you're wrong. Shut up when you're right." -John Gottman (This man knows a LOT about what helps - and what hurts - relationships. He's done tons of research on it, read his stuff it's amazing.
I like people who I can occasionally have really deep conversations with, and at the same time joke around with them. One of my best friends I can do this with. She is very wise but also knows how to make me smile!