Licensing your music, like many things in life, is a bit of a numbers game. Not everything you write will get placed, even in you have the greatest connections in the world. However once you make the right connections it's fairly easy to keep duplicating your initial success. If you get one song placed, getting your second placement will be that much easier as will your third and fourth and so on.
Success breeds more success. The first placement is usually the hardest, but subsequent placements become easier. This is true for several reasons. Number one, if you've found someone who has been able to place your music, they'll generally pitch your music that much more agressively knowing there is a market for what you do.
Secondly, supervisors will often times re-use tracks they've licensed in future episodes. Some placements are one time occurences, but often times your songs will be re-used down the road, generating additional royalties.
And finally, the more success you have in the industry, the more you learn about the industry and develop a sense of what works and what doesn't. You start learning about more opportunities and once you've had a couple placements under your belt it becomes that much easier to get supervisors and publishers to listen to and consider your music for future placements.
