Finding out exactly what we ought to do, in a positive sense, is often difficult. This is particularly true in a world, like the one we create, in which everything is, in a very real sense, "possible."
We can direct our power of choice in positive directions by heading off efforts to go down paths we decide we should not (for whatever reason) pursue. This works on both the personal and the political level.
I decided, as I entered adolescence, that I was not going to drink, smoke, or take drugs. Period. Never did. Never had to think about it. Arguably, this decision resulted in sending my life into directions that I now decide, looking backwards, had a lot of merit. But the decision wasn't based on a positive choice, just on a decision to say "No."
In politics, if we are willing to assassinate foreign leaders, bomb cities into extinction with nuclear weapons, employ the techniques of torture, and displace the governments of other nations when it's convenient for us, we will have a lot of choices to make about where and when these possible techniques might be employed. Arguably, we'll make some big mistakes as we try to figure out what to do (even if such political acts of war and terror are ever justifiable at all).
I argue that we would have a more positive politics, and better personal lives, if we would spend more time deciding just exactly what we won't do, as opposed to trying to figure out what we will do. The positive choices that can take us to where we want to go are a lot clearer when we we have already decided where we are not going to go.