Reading and understanding theory - having a cohesive ideology and understanding how you got to those positions. Then you can have a conversation, see where you came from, and lead them to where you are through a thought process. And also not be concerned if someone doesn't think the same way.

The big part of that is to understand that there is a wide range of opinions on the left, and though we all have the same goals, it's fine for people to have disagreements on details.

The discussions are not about convincing each other, but about introducing your ideas and learning from others to further refine your viewpoints.

Anyway, hope that helps.