Most essential things have already been said.
Never play out of your comfort zone, stakes-wise. Consider the money already "lost" right from the start, for the sake of your entertainment; the money you would happily give to a restaurant or bar.
When on a bad beat, always remember your lucky streaks.
If you make a major mistake and loose a lot, don't you ever attempt to break even in that specific session. It's all a life-long session.
If you 're rally tilted, stop playing immediately (not an option, unfortunately, if you 're the host).
Regarding physical tells, especially among people who have known each other for ages, it's much harder to conceal disappointment than joy.
So, I always adopt at the table a standard austere, sorrowful, yet peaceful expression, trying to copy Lord Jesus' look in His eyes, as portrayed in Churches' Domes.
