Talk to them about how to be friendly and outgoing. Most people drink, experiment with drugs and pretend to have seen movies that they haven’t actually seen, because they’re socially nervous. The best skill your child can have when going to a party is the skill of making new friends.
The basics are —
Smiling at people
Saying “Hey, my name is _____.”
Asking someone what their name is
Grabbing ice out of someone’s glass, throwing it on the ground, standing on it, then smiling and saying, “I guess that breaks the ice.”
Combine those for a friendly combo. Be careful though, don’t pull their name out of a glass, say “Hi” to some ice, and smile at the ground while standing on them.