The short answer is - with great difficulty.
If management has been slack at implementing policies and processes for so long, then you face an uphill battle.
The simple fact of this is that if management are expecting you to develop and implement a policy without backing you to the hilt, you are doomed to failure.
Management have to meet with all the staff, and tell them that things are going to change. But they also have to tell the staff WHY things are going to change, and how that will benefit the staff. Staff will resist any change when they are not told the reasons, and more importantly, what's in it for them.
You are a long, long way off developing and implementing policies. Your first actions are to prepare the ground and get the staff onside. This is going to take a lot of consultation and discussions to change the mindset of the staff.