Have core values and principles guide your decisions. If you have those in place, whenever you face a specific circumstance which goes against your core values, you already have an answer of what not to do. The potential downfalls will be gray areas though. Be careful to react to events which do not have a clear answer. Try to prolong making a decision, if possible (especially an irreversible decision for something large). Gray areas can be portals to bad decisions.
One thing that you can do to minimize making bad choices is perform the “grandma test.” The grandma test is simply asking yourself if you would feel comfortable or proud telling your grandma what you just did. Are you embarrassed or ashamed by your actions? Would you not want to tell your grandma how you acted in a particular situation? If so, it does not pass the grandma test and you should not do that.