When you are a new writer, one of the hardest things is to be open to criticism. After all when I was still learning, I didn’t understand the concept of editing. I wanted everything to be good on the first try. This is rarely the case. The more you write the more you learn that criticism is a positive thing, that it is what can help your writing get to the next level.
The other two aspects of improving writing mentioned in this quote are also key. Writing is important, but new writers often overlook reading. The more you read the more you know the power of writing, the more you understand how words can be manipulated.