Divide and Unite
Nothing unites people like a common enemy. Stoke the fears of your underlings by rallying them against a foe, and don't be afraid to invent one if necessary.
Saddam Hussein hadn't been in power long before he moved troops across Iran's border. Kim Il-sung had just established North Korea when he declared war on his southern neighbors. Sure, both of these leaders lost their conflicts, though they pretended they won—but that's beside the point.
War is expensive, so consider targeting an abstract enemy instead. It's much cheaper, and the beauty of it is that an abstract enemy can never truly be defeated. Hitler blamed everything on the Jews, Lenin targeted the bourgeoisie, and Communist regimes often turned on their own comrades.
The true mark of a successful dictator is when citizens are willing to report their own family members to the secret police for thought crimes. But once you've identified your enemies of the state, the question arises: what do you do with them?
Punishment is essential to flex your power, but if you're too public too soon, the culture of fear could backfire and shorten your reign. Disposing of enemies in secret works well, but so does giving them power.
Take a page from Zimbabwe's Mugabe. Unlike the typical dictator who might eliminate rivals, dissenters, and anyone who posed a threat, Mugabe took a different approach. He gave them power and riches, effectively bribing them for their support. If you can't beat them, make them join you.
So, when the colleague who was criticizing the new boss yesterday suddenly becomes your team leader the next day, take note