12 months old was the stage where I started thinking hard about education. The fact that my daughter was walking and discovered she could do many things and also found her voice
The key is that they model what you do and how you react. I'm quite firm with my baby but there's no screaming and I've rarely given her a spank. But it takes a lot of consistency: always explaining the rules, bending down at their level, not expecting too much from them (i.e. you know there'll be a meltdown at some stage if they miss on a nap or you take them out for too long or if they're bored...).. and limiting how many times you say NO, as this is unbearable for the child if he hears no all day! Rules have to be strict otherwise the child will test you.
Oh, and diversion is what works the best at that age.