Colonize a new place. Claim that the ‘others’ who were there before were simply savages and barbarians. Claim them as less than human.
Establish government and write the laws that favor you. When ‘others’ disobey the laws, throw them in jail. When the ‘others’ are forced to disobey laws due to conditions that only support people adhering to your way of life, throw them in jail. Claim that they’re in jail of their own doing, rather than due to any sort of system.
When you become the majority, hold onto that majority by any means necessary. Halt any sort of immigration so that you can claim and hold the majority power. Use majority rule as another basis to perpetuate your way of life.
Silence opposition by alienating ‘otherness’. Encourage those who ‘assimilate’ and ‘integrate’, and push those who choose to practice ‘otherness’ out. Use majority and legal rule to do this.
A uniform population is easier to control. Diversity leads to diversity in thought, which only heightens the risk that people may disagree with you and take you out of power. Do everything in your power to make that disagreement seem divergent to nationalistic ideals. Make those who dissent seem like they’re against your government. Appeal to those who agree to take out the ‘others’ and to dissociate with them.
Remember, power over human rights.
Constantly evolve. You never know when your next threat will hit. Take care of it before it even has a chance to rise up.