Teaching is a vocation, a calling. It is like being a physician, a parent or a priest. You have to live and breathe it, every moment of every day. It's an awesome responsibility, second only to parenthood, in my opinion. Also, teach what you love and show students your own enthusiasm for life and learning.
Classroom management is always a challenge.
I tend to be more flexible with my lesson plans, letting good discussions go on, etc. I think the best classroom management technique is a good lesson. The days I struggle are the days I'm not adequately prepared, or the days that my well-planned lessons fall flat. I think that's a negative attitude that teachers reinforce to their detriment. We bring it up to each other, to parents, and to our students.