Even if you've used Google Docs for years, you may have overlooked several useful add-ons, including:
Hold a conference call without leaving the document (with the "UberConference" add-on).
Insert accents for 20 languages directly from the sidebar (with the "Easy Accents" add-on).
Table of contents
Quickly jump from place to place in your document directly from the sidebar (with the "Table of Contents" add-on).