My writers' group colleague, Nancy Tandon, has just sold her first book. From Publisher's Marketplace:
"Nancy Tandon's SAY MY NAME, in which two speech-therapy 'rejects' draw
strength from heavy metal music and Muhammad Ali as they search for
their true voices, to Rana DiOrio launching Big Dill Stories, in a nice
deal, for publication in Fall 2017 (World)."
Nancy is a member of the Society of Children's Book Writers and Illustrators, has attended its programs, and is the moderator for our writers' group, which is sponsored by the New England SCBWI. In addition, she's been a finalist for the Tassy Walden Award. In fact, I believe she's been involved with that award more than once.
My point being, she has been training as a writer for a while now. This sale didn't just happen, didn't just drop in her lap. She worked for it.
That's how it's done.