You need standards for work quality, timeliness, and cooperation. You need to communicate those standards. And you need to maintain them.
It’s easy to make an exception for this and then an exception for that and another exception for something else. It seems like a good idea at the time. But if you do that too often your standards become the exception.
This is only one of 347 tips in my ebook, Become a Better Boss One Tip at a Time.