Machiavelli's advice is very specific in telling the prince the right way to rule his state. Machiavelli is also very specific on what things the prince should be familiar with such as the art of war and how important it is to maintaining his power. Machiavelli does not encourage the prince to fallow or accept a specific ideology but the set of ideas Machiavelli gives the prince in a way are there own ideology. Machiavelli does not try to make the prince think in an ideological way. He tells the prince to be aware at all times of what is going on around him even in times of peace. For example, the prince is encouraged to scout all his territory many times over even in peacetime so if the time comes he will be ready for any type of attack that might occur. If the prince thought ideologically, he would not worry about things that were not happening at that exact time and in turn would not be prepared for what is to come. .
The prince cared to some extent about his people and did not want them to live in fear due to the negative effect living in fear might have over a long period. On the other hand, the ideological government does not care about the people, it considers them nothing and only worries about the state, and this causes the people to live in fear. When enough people live in terror they will always try to fight back and try change things so they do not have to live in terror any more. One thing Machiavelli and Nazi Germany might have agreed on is the means does not matter as long as the result is in best interest of the state. Machiavelli and the Nazi's did not care what they had to do to get what they wanted as long as the purpose was good for them and the state.
When it comes to the prince's relation to the law Machiavelli encourages the prince to act merciful in public. When in public, the prince stays well within the law in order to please the people but in order to keep the state running smoothly he must be above the law in reality.