I remember back to my first year or two of teaching in Korea and how clueless I basically was. Like I almost literally had no idea what I was doing and what was effective, or not in the classroom. It didn't help that my school owners were business people and not teachers and so could offer no really helpful guidance except don't sit down and make sure you smile.
If I would recommend one book for a newbie teacher to read, it would be this one: How to Teach English by Jeremy Harmer. It contains some theory that is very accessible and not really academic and then has a multitude of practical and helpful tips for things like lesson planning, classroom management and activities and games. Even experienced teachers would find it useful I think.
If you want to get a University Job in South Korea, check out this Ebook.