Another good book ...
Shepherding A Child's Heart has to be the best book out there. My wife and I have read that many times and we love it.
Another good book is, "To Train Up A Child" by Michael and Debbi Pearl.
http://www.nogreaterjoy.org/
They aren't Ammish but live in the community. They take a stricter lean on discipline (spanking) than what my family does but the book is great. We do spank and believe in it but they go the extra mile, per se. That is fine for them and other parents may not spank as much as my family but that is up to the two of you.
It is a cheap book and short.
One thing we do as a family, as others do I'm sure, is to #1 never spank in anger. I did once and had to get on my knees and beg my daughter for forgiveness.
Ask them why they think they are getting a spanking and let them know if they don't know. Let them know how many they are getting (some like more in number swift spankings, some like fewer powerful spankings). We always have a time of restoration, per se. Love on them. If it is a sin that was committed then they not only need to be displined by you but they sinned against the almighty and sovereign God, the One who created them.
A good thing that we do as a family is role playing, per se. We practiced many times before we brought our children into the Church service. Probably about 15 times of sitting in a folding chair beside them while they colored, read and sat quietly for what we built up to be an hour. We can tell our children how to act but it is a little easier if we practice it with them. Shaking hands and acknowledging someone when they speak to your child. Have someone practice that with them. Looking into someone's eyes when they speak to them, etc. etc. It takes time out of my day to do this but it isn't mine to begin with.

And what better investment to make than teaching your children God's Holy Word. We also have a box shaped as a heart that we put our memory verses in after we learn them with the children. So they can hide it in their hearts.
Sorry, I seem to defend myself a lot at work when things like this come up with parents who want to be their children's friends first and foremost.