Substitue teaching will do three things for you (unless you have an experience like the fellow from Florida). It will give you valuable classroom experience, especially classroom management skills. Without these skills there is no way to be a successful teacher. Second, it will allow you to view a range of grade levels and give you a sense of where you belong. Thirty odd years ago I thought that I was going to be a high school teacher of english. After subbing for a kindergarten teacher I recognized my true love and calling and have been a kindergarten teacher since then (having pursued a masters in ECE). Third, you will get to network with teachers, get inside information and, hopefully, impress administrators with your skill as a teacher.
Eric Gidseg, Ph.D.
Pleasant Valley, NY