I see lots of managers struggle with making decisions because they want to get all the information so they can make the "right" decision. Very rarely will a manager be able to make a decision with all the information. Get comfortable with that.
Annie Duke, professional poker player and author, writes some of the best thinking on this topic. In this book, she discusses how poker players have to make decisions based on odds without knowing all the information. There are two parts that I think are most valuable to managers.
First - Resulting. Resulting is when you let the result of the decision determine if the decision was good or bad. She correctly points out that good results can come from bad decisions and bad results can come from good decisions. The one individual result doesn't matter, what matters is if you made that same decision in the same situation, how many times would it be good or bad.
Second - the after action review (although she doesn't call it that). She talks about how great poker players review the decision making after the games. They don't just focus on the hands they lost, they focus on the hands they won. And they do so dispassionately. Each decision is up for critical review, because you can learn something from it.
Reading this book made me a better decision maker.
Note: Mrs. Duke has a new book out - How to Decide. I will be reading this one soon. If you've read it, let me know your thoughts.