Some advice on how to help your kid become a good writer from M. Molly Backes, via Ta-Nehisi Coates:

First of all, let her be bored. Let her have long afternoons with absolutely nothing to do. Limit her TV-watching time and her internet-playing time and take away her cell phone. Give her a whole summer of lazy mornings and dreamy afternoons. Make sure she has a library card and a comfy corner where she can curl up with a book. Give her a notebook and five bucks so she can pick out a great pen. Insist she spend time with the family. It’s even better if this time is spent in another state, a cabin in the woods, a cottage on the lake, far from her friends and people her own age. Give her some tedious chores to do. Make her mow the lawn, do the dishes by hand, paint the garage. Make her go on long walks with you and tell her you just want to listen to the sounds of the neighborhood. 
Let her be lonely. Let her believe that no one in the world truly understands her. Give her the freedom to fall in love with the wrong person, to lose her heart, to have it smashed and abused and broken. Occasionally be too busy to listen, be distracted by other things, have your nose in a great book, be gone with your own friends…
Let her go without writing if she wants to. Never nag her about writing, even if she’s cheerful when writing and completely unbearable when she’s not. Let her quit writing altogether if she wants to.
Let her make mistakes…
Keep her safe but not too safe, comfortable but not too comfortable, happy but not too happy…

TNC sums it up beautifully: 

Failure and boredom are underrated forces for good in this world.