Model and teach appropriate social behaviors. Many abused and neglected children do not know how to interact with other people. One of the best ways to teach them is to model this in your own behaviors, and then narrate for the child what you are doing and why. Children see, hear, and imitate. Over time, success with other children will make the child less socially awkward and aggressive.
Maltreated children have problems with modulating appropriate physical contact.
They don't know when to hug, how close to stand, when to establish or break eye contact, what are appropriate contexts to wipe their nose, touch their genitals, or do other grooming behaviors. Adults misinterpret this as affectionate behavior. It is not. How adults handle this inappropriate physical contact is very important. It is important to make these lessons clear using as few words as possible.