3. Hunt down duplicate items
Copied files can cause havoc with your favorite playlists, to avoid this Open up the View menu and tap Show Duplicate Items to see matches with the same song title and artist name. Hold down the Shift key (Windows) or Option key (Mac) while opening the View menu to access a more exact duplicates option also based on album name.
Keep in mind that the search is only applicable to the current playlist or view. If you do not correctly fill out the metadata associated with your songs then you must bring up column headings like track length and file size and sort your library using these criteria to try and spot tracks that are the same.