The flip side of knowing when you are wrong is knowing when you are right. This one is much harder, more rare, and needs to be enjoyed (because of it's rarity).
You know when you are right the same way you know when you are wrong, you just know. It is a cognitive reality. Sometimes you will know right away because your conscience hasn't piped up (hopefully yours still has a voice!), this is a great a refreshing place to be in. Other times, knowing when you are right will take years to show itself.
Take, for instance, my decision to go back to school after being married four years. I think (cognitively) that I made the right decision, but a part of me is waiting to declare victory until I graduate and am working in my chosen profession (hopefully teaching the Bible somewhere). My conscience hasn't said I'm wrong and my cognitive abilities have given me a lot of hope. Also, I am simply trusting God.
I made a very thought out decision with my wife and a few close friends and family members, and looked at what a college education will give me (skills to get into a career that I will have passion for). I made a careful decision and all signs pointed to, "this is right." Now, in the midst of it, I'm trusting God.
Long answer. Hopefully you see what I'm saying.
How about you? When do you know you are right?