...you can control anything.
First, you have to get people to listen, then you have to show them that what you are saying is true. After that, you have to make them believe it is something they want to be a part of.
The next step is to control the media. Control what information people have access to, and how they think about it. Make sure that only information that supports your beliefs is accessible to the public. Censor anything that could potentially undermine your authority. Create an environment where scepticism is not allowed and where people are not allowed to question your authority. Then create a system of rewards and punishments for people who do believe in what you want them to believe and those who don't. Make sure that those who toe the line are rewarded with power, status, and privilege, while those who don't are punished.
Remember that people are emotional creatures. This means that you have to appeal to their emotions to get them to believe in what you want. The best way to do this is to tell a story that will resonate with them on an emotional level. Stories are powerful because they can bypass the brain's rational part and speak directly to the emotional part. Constantly reinforce your message. Use every opportunity to remind people of what you want them to believe, and why it is important. Make sure that your message is the only thing that people are exposed to, and that they hear it over and over again.