Both answers so far are good. Especially the info about having great songs.
I think it's so competitive out there that my suggestion to you is to focus on developing relationships with artists you believe in. If you write songs with them and they value your writing contribution, you will have a chance that they will cut your song or songs. Yes there are song pluggers and publishing deals. But ultimately it is about the steps you take to become good at what you do and to be proactively selling them in a way that fits your brand and isn't too pushy. And it's about becoming of value in the co-writing experience.
Unless of course your songs are insanely amazing. Actually even when they are, you still need believers to want to cut them.