When you get down to it, the only way you’ll improve as a writer and become good at writing is basically and it’s real simple.
WRITE, WRITE and WRITE
Rewrite some more.
Develop your skills, discover the genre or genres that you're passionate about, develop your own unique voice, writing style and put your own personal trademark into your writing.
Don’t forget to read everything and anything, watch movies, read screenplays and put your work out there for feedback.
Build up a body of work, create a website, take yourself seriously as a writer and market yourself.
You might have written a thousand novels, screenplays, but if no one knows you’re a writer, how do expect to get noticed?
But most importantly WRITE.