What is some advice you can give for someone about to meet their girlfriend's family as an adult rather than a teenager?

It's been 9 years since I was last introduced to a significant other's family, and since then it seems the stakes have gone up because we're no longer young adults with few expectations and unlimited potential, but instead adults with a developed personality and life outside of our parents.
What is some advice you can give for someone about to meet their girlfriend's family as an adult rather than a teenager?
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