I would ask if you could observe or volunteer in a friend's classroom to get the jist of everything, see if it's right for you. I got my degree in Deaf Ed, but decided not to go the teaching route after having to take a semester of observations before entering the school of ed to get my credentials. I'm a homeschooler at heart, I couldn't stomach the idea of not having one on one time to work with students.... plus all the politics and stuff.
Unless you're doing long term subbing, you're not going to need much more experience than being assertive and being able to improvise no matter what kind of instructions the teacher leaves for you. I think your biggest obstacle is going to getting on the substitute list for the school district or school. In the Central Valley, most of the larger school districts froze their lists two or three years ago. Teachers that are surviving layouts are being kept as full time substitutes. Keep in mind that even if the lists are open for your area, you're going to need to pay for things like finger printing, background checks, TB testing, etc just to qualify to get on the list. After that, it's a matter of getting your name out there and gaining a good reputation so that teachers will request you. My mom always requested the same sub, with maybe two others as alternates. I can only remember a few times where she just put it into the system for anyone to show up.
Good luck!