One more critical communication and interpersonal skill that I've picked up: Assumptions often drive behaviours. Getting to the bottom of those can significantly change the outcome of a project.

I've adopted the following table both personally and at a project level in order to keep track of changing assumptions. At the beginning of a project level-setting on assumptions can enable an open working relationship and resolve a large number of issues before a project even begins. Monitoring those assumptions can quickly give you a good sense of the the project's level of success (If  everything that started in the "What you fear" moves into the "What you know (or think you know)" column, you are probably in trouble. )