Celebrated authors from Stephen King to Michael Moorcock and everyone in between have expounded on the basic tenet of writing: reading.
I can't overstate this enough.
When you start reading in order to improve your own writing, you read in a different way. Personally, I've been more attentive, more critical, more of everything really, rather than just reading passively or for pleasure only (though science fiction is always a pleasure for me to read).
The more I read, the more I understand and can see underneath the story to its skeleton and the layers upon layers that make the story what it is. I can almost feel the understanding of storytelling settling into my mind.
So, I can tell you from experience, the best way to improve your writing is not just to write, and write every day, but also to read, and read every day.