I agree with Epic.NameX2. While I naturally draw down the moon, I assumed that my primary working element would be water, but I actually find that I can manipulate fire rather naturally and with little effort without spell work.
Just quiet your mind to the world and let the elements call to you.. You will feel a pull to one more so than the other.
Frannyboy is right on some level, you do work with all the elements and some can even manipulate more than one naturally without spell work, like myself(fire and air). This isn't something that I now of to be the norm, however, so please don't be frustrated if it doesn't happen.
But I believe through study, practice and establishing a relationship with Nature and her Devas (spirits) it's possible.