Rome learned a lot from the Greeks. As a result, it many good policies and practices. This helped it to survive many a bad emperor. Romans also had a very strong sense of honor. Like the Japanese, if you disgraced yourself or your family, you were expected to kill yourself. We can debate the morality of that particular tradition, but methinks it kept their elites on the straight and narrow. [Their mass conversion to Christianity may have weakened this, IMHO]
You also have to remember that the velocity of information back then was very (very) slow compared to today. The reputation of Rome kept her great even after she had rotted internally. Eventually, a few smart barbarians figured out that Rome had become a paper tiger. Even after her fall, it took decades for the word to get out that the Empire was indeed gone for good.
I would add leaving the local authority in place alongside a Roman governor. Taking the kids of the leader to Rome for education and imposing Roman law. I took a strong lesson from the strength and spread of Roman law, that I highly object to the exceptions we see for those inside the beltway.