Doing good in response to those who do some good to us is inherent in man. And it is not difficult. Because they have been good to us before and our good deeds, in fact is a response of their favor.
The main point is this how should we treat those who have not been good to us? Should we reciprocate? Apart from some special cases, for example when doing good can be abused by others, Islam recommends to kind treatment. The Holy Quran says: “Let them forgive and overlook, do you not wish that God should forgive you?” (24:22) and as you, forgiving others is one of the grate examples of good deeds.
But why we should treat kindly with those who have not been good to us? First of all because your action reflect your conscience, if you do good it shows your good conscience and vice versa. “Everyone acts according to his manner.” (The holy Quran, 17:84)
in a very interesting tradition, Prophet Muhammad (Peace Be Upon Him and His Progeny) has said: “Treat with kindness those who are worthy of it and those who are not worthy of it. For if you treat with kindness the one who is worthy of it, then he is worthy of it. And if you treat with kindness one who is not worthy of it, then you yourself are worthy of it.” (Usul al-Kafi, v.4, p.27)
Yes dears! You are worthy of kind treatment. So, do it.