You may have easier access to other books and papers which will serve the purpose as well. Effective contracting depends upon effective communication skills. If you wish to go deeper than that, it is worth pursuing both expressive and listening skills. You might begin with something on assertion. You can follow it up with something that emphasises the listening aspects of communication, for example any of the effectiveness training books by T. Gordon.
Conflict can arise suddenly.
So it helps if you have some conflict management skills. There are two books on a gestalt approach to consultation which I have found very useful. Though their book is not recent, Hermann and Korenich offer very practical advice on developing a healthy relationship. Nevis describes a style of relationship and presentation which can have high impact. Activities A thought experiment Choose some relationship which is ongoing, and in which you and the other person have very different roles.