A frequent comment to me-- "I suppose that when you go into a new assignment you find lots of bad decisions have been made!"
No that's typically not the case; rather previous management didn't make any decisions--there was a backlog. An organization suffers more from the lack of decisions than from bad decisions. Why?
With bad decisions at least you learn; you get feedback; you have a frame of reference; the middle managers in the organization at least have a direction. With no decisions little is learned; you get no feedback; you have no frame of reference; and middle managers have no idea what to do.
In your first 100 days in a new assignment, make sure you clearly identify the key decisions that must be made, make them, and communicate those decisions clearly and continuously to your managers. Sometimes they're tough and you're tortured; how do you deal with that?