Most people I know have used iTunes for a long time. If you're one of them (as I am), you likely would have accumulated a LOT of music, and chances are, there are quite a few duplicate songs in your library as a result. This is common since some artists will feature a particular song on more than one album. This is fine at first, but over time, those duplicates can really add up to a significant chunk of hard drive space.
There are two ways to correct this problem: 1) the hard way and 2) the easy way. If you're like me, I prefer the easy way. Regardless of the method, the process is simple... identify the duplicate items and remove them from your library.
The Hard Way
For those who prefer the hard way, the process is simple (notice I didn't say "quick"). First, you need to list all songs by title. This is most easily done by clicking on the "Songs" tab in the "Music" section of iTunes.
Now that you can see a list of all music, you will want to sort by title. This can be done by clicking on the "Name" header. Click once to sort A-Z. Click again to sort Z-A.
Once the list is sorted, simply scroll through the list, highlighting the duplicate items, and deleting them.
A slightly faster way to identify duplicate items would be to use the built-in duplicate item filter. This can be activated by going to View > Show Duplicate Items.
The resulting view will list all items that are considered a duplicate. As with before, you will want to scroll through the list to locate and delete duplicate items.
The Easy Way
Where there's a will, there's an app. "Dupe Away" is an inexpensive ($12.95 USD) app that is simple to use and effective. Simply run the app, and it will find all duplicate items in your library.
Once the initial analysis has completed, you are presented with a few options to clean up your library. As you can see here, Dupe Away has identified 1,556 duplicate items, accounting for 2.2 GB of wasted space!
When you're ready to see the list and start the clean-up process, simply click on the option you want to explore. The rest is super-duper simple!
If you want to give Dupe Away a test drive, they offer a free trial version that will show you the duplicates you have on your system before you lay down the money for the full version.