First and foremost, I am aware of the existence of this question - How do I add a library project to Android Studio? - and unfortunately, it has not helped me.
My go
For Android Studio 3.2.1:
Click the File/Project Structure menu (ctrl+alt+shift+S). Press the + button in the Dependencies tab from the app menu to add a Library dependency.
Look for com.google.guava:guava:(whatever number is the most recent one) and add it.