I agree the the best way to try to avoid another Hitlerian experience is by learning from it. We need to be able to notice the signs early enough so that we can detect it and prevent it from happening again.
I think that it is inevitable that there will be leaders in the future (and there are some right now) that would love to dominate the world in a brutal way such as Hitler did. This is why the United States, along with other countries, need to be firm and aggressive when dealing with these kinds of countries.
In addition, there are many countries who believe that their culture is the only culture that should exist in the world. They believe that all others should be demolished. This is why we need to spread the concept of acceptance, especially when it comes to accepting people who are different from ourselves.
It is also important to note that we have not entirely avoided other "Hitlerian" experiences, as dictators have taken over numerous countries since and perpetrated war and genocide both. So it may be impossible to avoid it entirely.
But one way to avoid a repeat of history is to study and remember it. We do a fairly good job of that where Hitler is concerned, and for World War II in general. We don't do as well at highlighting the events in places like Rwanda or Darfur, and therefore we endure repeated tragedies.
Another way to avoid a repeat of that catastrophe of a human being is for the world to commit to, and react to the future Hitlers of the world who take power and aggression. Hitler was appeased in Czechoslovakia, and it failed miserably. We should be careful not to repeat that mistake when a true threat, a real Hitler, rises to power.
To put it simply, if we could teach students to "not believe the hype" and encourage the kind of open and honest debate that we've often thought was part of our national discourse, it would be easier to avoid something like that in the future.
One of the difficulties that will make it easier for men like Hitler to grab power is the fact that we are pushing towards a great deal of standardization in everything we do, particularly in schools. We want to train teachers the same way, we want to train kids the same way, we want to be able to predict the way that people will react, something that will make it much easier for someone to manipulate them.
When you look at the fact that there are very few strongly dissenting groups of people, particularly groups that aren't spouting some version of the main stream media's talking points, it is not hard to believe that it will not be really difficult for someone to take advantage of that fact and rise to power by pushing the right buttons.
Again, to prevent that, we need to change the way we look at education and find ways to encourage students to investigate things they are curious about instead of trying to craft a standard curriculum that dictates what everyone will or should learn and when they ought to learn it by. Trusting people and in this case young students to make decisions for themselves is not something that comes easily to us, but when you look at the alternative and consider that it might end up being someone making the decisions for them... Perhaps it becomes more of an appealing option.
I think there are a few of ways to do this.
First, I think that it is important to spread the values of tolerance of other kinds of people. I think that the more that this becomes a norm, the less possible it will be for another Holocaust to happen (though we have failed to do this so far).
Second, we have to work to make sure that countries do not find themselves in the same situation Germany was in after WWI. We have to try to be sure that countries do not get to that same point of desperation that allows them to choose a demagogue like Hitler for a leader.
Finally, we can be more vigilant about leaders who look like they might be trying to expand like Hitler was. We can be more aggressive about making sure they are not able to start taking more and more territory the way that Hitler was (Austria, Sudetenland, etc).