Collaboration means work on a file together. Whether at the same time, or at different times of the day, Google's collaboration tools (Comments and Suggested Edits) removes the needs of multiple copies of a document as it gets sent back and forth between collaborators.
In this new video from Google, you'll see the best of the collaboration tips in action. Specfically, Comments and Suggested Edits, Notifications and Revisions (ie. versioning).
Another tool that is often under-used is the Email Collaborators command from under the File Menu. The best part is that it automatically include a link to the document you are currently working on.
What's your favorite collaboration tool?