There are many resources for helping children learn social skills, and they may be readily used at home with parents providing plenty of context and discussion about application of the ideas, as they go through the process of teaching their children.

Here is a brief roundup on direct teaching of Social skills (body language, friendship, etc)
- book: 100 social rules for kids (hat tip to sanne)
- direct teaching of non-verbal cues
- direct teaching of friendship
- direct teaching of perspective taking
- link to an article on the Davidson Database, Tips For Parents: Gifted Children's Friendships
- post with roundup of articles on friendship