Today, a quick tip: Once you start submitting your music to companines working in the licensing industry keep a a spreadsheet of when and to whom you've submitted your music. Then, about three to four weeks later follow up with a phone call or email to both make sure your music has been received and to see whether or not they've listened to your music and to see what they thought. Don't just sit back and forget about it and assume the ball is in their court.
Now some companies actually have a "don't call us we'll call you" policy and of course if that's the case then you should respect that. But that is not generally the case.
I keep a spreadsheet of all submissions I make that includes the date, where the music was submitted and to who it was submitted. Then three or four weeks after the submission I follow up and make a note of whatever response I get. Sometimes there is no interest, sometimes there is an invitation to submit more music and other times there is a request to follow up a few weeks down the road. Whatever the response is, I document it and then follow up accordingly.
Why follow up? Well it communicates all the right things. It demonstrates that you're serious about your music career and that you're determined to make things happen. It also helps to simply remind the recipient of your music who you are. In the fast pace world that is the music industry this sometimes makes all the difference. I took the ball and followed up on the song that ended up being my first placement and signed a contract within a week! So don't be afraid to be persistent.