Firstly, you'll want to be registered with a PRO (Performance Rights Organization) like ASCAP, BMI, or SESAC that can collect money on your behalf whenever songs are placed on the radio.
Next, you'll want to register your releases through services like Tunecore.
Tunecore collects about 50% of royalties that your PRO doesn't. Your mechanical royalties and direct licensing royalties can make up a good portion of your income if your song starts to pick up traction, so be sure to sign up with Tunecore in the button below and pay the one time $75 fee in the Music Publishing section.
They let you submit as many tracks as you want with the one time fee for licensing opportunities with TV, Film, and more.