I am a writer, and the best advice that I could give is to write and find an outlet for your writing so that other people can see what you do. Whether it be a school paper or a blog, write and get people to read it.
I have been writing for ten years. My advice is to write every day even if all you're writing is a journal entry. Seek out critique and take what's helpful, leave what isn't. Ultimately your writing is yours and you should only change what you feel should be changed.