"Good" and "successful" may not be the same thing.
E.L. James, the writer of Fifty Shades of Grey, would generally be considered to be successful, but her writing (in writing circles) is considered to be very poor. She just hit the write market at the right time.
How to be good:
* Read well-written books.
* Write daily.
* Critique others so you learn how to critique well.
* Rewrite your own work.
* Get others to critique your work and rewrite again.
* Keep writing.
How to be successful:
* Get a lucky break.