Here are the three key steps to any culture change.
1. Are you sure you have the right people?
If not, either lose the ones that must go, or fully commit to who you have.
2. Do you have clear expectations?
Do people understand what constitutes a fireable offense? What is required and what is optional?
3. Do you have agreement?
We assume agreement when it may not be there? Did you confirm people have explicitly agreed to do what you asked? And can they say no or challenge you?