Never, ever say you disagree! Instead, use the Agree, Build and Compare framework from Crucial Conversations to arrive at agreement. This technique avoids getting dug-in with a defensive posture that leaves you no where to go in the conversation.

This video is based on this article that I wrote:

https://jameswilson.io/agree-build-and-compare/

And the work of Kerry Patterson, Joseph Grenny, Ron McMillan and Al Switzler in Crucial Conversations: 

https://www.amazon.com/Crucial-Conversations-Talking-Stakes-Edition/dp/0071771328