Figure out how you wish to use the music and the terms of your usage. How and when will the song be used? How long will the piece be (the term)? How much are you willing to pay? What kind of territory will you want rights to (just the United States, or North America or global)? What's the purpose of your film; is it educational or commercial?
Figure out the rights you want. The easier and more expensive way is to negotiate for all rights, but if you are simply using it at a film festival or not releasing it theatrically, you can negotiate for individual rights such as nontheater rights or television rights.
Find the publisher and obtain contact information. To clear an existing recording, you'll need to find the company that owns the master recording. To get this, look for the publisher on the music's packaging or find the song's information on an online database such as BMI or ASCAP (see Resources).
Contact the publisher. With your contact information obtained, give the publishing contact the information on the piece of music you want to use (song, writer, publisher, song length and term).
Make a deal. If the contract terms brought back from the publisher are satisfying, pay the agreed-upon price and use the music.