If you’re still in college, I’d recommend taking more writing classes. Practicing writing and getting feedback will help you improve. It’s also important to read a lot. Read books, read the newspaper, and read other people’s personal statements to get an idea of how they’re written.
But in my opinion one of the best ways to become a better writer is to read bad writing. Just as some people maintain that you can’t feel happiness without ever having been sad, it’s hard to appreciate good writing if you’ve never read something terrible. This can also be done in class since in my experience many writing classes encourage peer reviewing. I’m not saying everyone in your writing class will be a horrible writer, but some will be, and everyone in it will definitely need improvement, otherwise they probably wouldn’t be taking the class.
So read your peers’ writing and remember that just as there’s no mistaking spoiled milk, you can’t escape the sour taste of bad writing. As you come across a particularly bad sentence, paragraph or paper, try to determine exactly what makes it so bad. And try correcting the sentence to make it better. In my experience this has helped tremendously.
And if you want, we can discuss setting something up where I can look over your personal statement. Good luck!