Simple, start with the most egregious offenders, Iran would probably top the current list. NK is of course on the list, but since they are pretty much isolated and don't really affect that much outside of South Korea, which has pretty good defenses of it's own and only needs our aid not us doing it all for them, then countries like Iran, who export and sponsor acts in other countries should have the higher priority. China, we are already addressing, or were non-militarily (we had a good working plan for awhile there, some one has just dropped the ball on it). Russia is not really that hard to address since a lot of it's problems actually stem from not getting their economy up and running properly. We could help them out with that, even have tried a few times, if they would let us. South America isn't really that big a deal either, a lot of their problems stem from our addiction to drugs. That is clearly evil happening because of our actions, but not our military ones. And we should stay out of civil wars unless it is against an allied government and sponsored/supported from outside that country. In Africa, Somalia would probably be first, it's piracy is causing too much trouble.
Many, many places don't really need intervention. Most of Central and South America, a large part of Asia. Their governments are not really evil or oppressive, just not effective economically. Even Venezuela, I don't agree with their current government, but as long as they are not murdering or torturing innocent people over political/religious beliefs, I don't see why we should tell them what government they should have. We should only be stepping in when it involves the government sponsored murder and torture of people or support of terrorist organisations. And then only after addressing it in other fashions.
Iran has had sanctions against it for a long time, they are not working. They have been offered technology for nuclear plants that would not allow the creation of nuclear weapons, but they have refused. They continue to sponsor terror in Iraq and have caused violent uprisings in other Muslim countries. They are currently supporting an oppressive regime in Syria.