I know you've probably had this one thrown at you so many times, but if he has a special interest/obsession, could you take him to a social group revolving around that?
But anyway, I've never found books particularly helpful. I just get flustered and forget everything I've read. The best 'social help' I've ever had was developing them in said specialist interest groups, roleplay with people and adults who understand my difficulties and are willing to do conversation roleplay with me, and watching as an outsider how people behave so I can mimic their behaviours. |^-^