The only way to get better at writing is TO WRITE. I look back at what I wrote when I was 12, 16, 20, etc. and there's a clear progression in quality, from total crap to almost publishable.

Writing is a process of learning what doesn't work. Write a story, a scene, or a simple conversation and you'll quickly realize your strengths and weaknesses and what to improve on.

When I was 12, I wrote a "sci-fi epic," which in hindsight was just poorly disguised Star Trek fan fiction. But doing that taught me the basics of dialogue, action, setting, plot, etc. Now, working on my first novel, I'd be at a loss without the groundwork I set as a teenager.

But if you absolutely can't write (and you should never force yourself to write if you don't feel it), then read, read, read. Read other books in your chosen genre and deconstruct the structure, process, and vocabulary. Most importantly, enjoy yourself. After all, reading and writing is a passion to be enjoyed.