Don't just write, but read. Read all the time, if you can, when you're not writing. I sat with an editor from a major publishing firm on my daily commute. She told me to make sure that I was reading. Not just to know what else is being written, but to know who I write like. We all want to say we write like ourselves. We all want to have a unique voice, and we should strive to do so. But publishing companies want to know who you write like.