Love and routine, definitely. I was at a mental health symposium the other day and they said something really interesting. They said that it's essential that parents engage in "serve and return" with their children. What this means is that the child will offer an opportunity for connection (e.g. cooing, reaching out physically, talking if they're older) and it's essential for the parent to respond to that in a loving, caring manner. Now, obviously, no parent is perfect, nor is every situation perfect (e.g. maybe the kids are pounding on the bathroom door while you're on the loo). But overall, there should be consistency in "returning" your child's "serves". This is essential in developing proper brain connections in children.
The other thing I believe is very important is to model the behaviour you want to see. If your child won't say "please" or "thank you" or is refusing to do what you as, check your own behaviour. Do YOU say "please" and "thank you"? Do YOU respond positively to your children? Children can smell a phony a mile away and they can quickly pick up on inconsistencies. If you show them "this is how we behave", then they learn from your example.