How can I become better at writing?

Read more and practice more. When reading, don't just read for the entertainment; try to constantly take mental notes on anything the author does that is particularly effective, and think about how you could apply it yourself. When writing, try imagining how you would tell the story out loud, then imagine how it would be different if someone else were telling the story (someone you know, or one of your favorite authors). Read your own sentences over to yourself in your head, as if you were reading the story out loud to someone, and pay attention to anything that sounds out of place, then think about how you might change it so it sounds right.