I’m a proponent of tagging notes in Evernote. If you are too, you might find this tip useful: Entering -tag:* into the search field displays all untagged notes. From here you can go through the results and apply the proper tags. I run this exercise a couple of times a month to make sure everything is neat and tidy.
Here’s what it looks like on Evernote for Mac.
Here’s Evernote for web.
You may want to consider saving the search for future use. To do so (on the Mac desktop app), go to the edit menu / find / save search.
Want to take Evernote search even further? PC World has six great tips right here.
You may also want check out BrettKelly’s Evernote Essentials e-book. Click this affiliate link to buy your copy.