Keep your mouth shut and see what's happening around you. Don't finish people's sentences for them. Don't just hear what they say, but also how they behave while they're saying it. That was great training for writing.
My sister and I used to act as maids and waitresses at my great aunt and uncle's cocktail parties, which were very much sort of retired, minor stars of the Yiddish theater and the Yiddish opera.
The great pleasure for me in writing short stories is the fierce, elegant challenge.