It briefly describes ways of stating your own point of view, and ways of getting information from others. It also deals briefly with managing the process of an interaction. My approach to communication skills builds on some of the models and processes of Chris Argyris. There is a summary of Argyris' core model on the arlist archive. 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.