Here's a quick method to clean up your tags. Open the desktop version of Evernote on your PC or Mac and scroll to the bottom of the side bar to select tags to view. All the tags you have used will be displayed along with the number of times that tag has been used.
Use CTRL or CMD to select all the tags with (0) next to them. These are the unused tags.
Simply right click and select Delete. Goodbye ghost tags.
This post first appeared on http://librarycurrants.blogspot.com/2015/11/tidying-up-evernote-tags.html