Yes, with an only child, we've taken the approach that we have to actively demonstrate cause-and-effect for our DD.
So if she does/says something that a peer would find unacceptable, we let her know that.
It's not always easy, because of course as loving parents who are emotionally mature, we do NOT necessarily have the kinds of knee-jerk responses that children do-- but, for example, if she's a sore loser in playing a board game, we demonstrate disgust and refuse to play the next time.
Stuff like that helps to build pro-social skills. As does talking about social dynamics, human motivations, etc. Basically-- be a student of human behavior and interactions.
As for friendships, being DISLIKED is a matter, IMO, of not-so-awesome social skills, not of giftedness per se. Being lonely, on the other hand, is a matter of being quite different from one's peers.
My DD has no trouble being well liked. In fact, it's often a bigger problem that she doesn't especially like those who adore her. She doesn't tend to have friends who "get" her completely, though she certainly has no trouble "getting" them. It is the one-sidedness of this that makes her feel lonely and sad.
For that, I don't have much in the way of advice.
