I would leave most governments in Europe, the Americas, Australia, and a good part of Asia in place and allow them to continue to govern themselves, except that I would be the highest power, similar to the position of the federal government over the state in the US, but more absolute. If I had to remove a government, I would merge the country with one whose government I was able to leave intact. The only major decrees I would make are.
1. Any of my subordinates who attempt to institute censorship will be put to death.
2. Malicious prosecution will carry the death penalty. Prosecutorial misconduct is a felony.
3. All citizens of my empire would have the right to bear whatever arms they could afford, with the sole exception of nuclear devices.
4. The manufacture of internal combustion engines will be banned. Owners of existing engines will receive a gasoline ration, and the production of spare parts will be permitted.
5. Any adult may marry any other adults who consent. A marriage may consist of as many people as will consent. Forcing a person to consent to marriage carries the death penalty, and is the only capital crime that may be carried out on a person who is not representing the government,
6. Citizenship may be revoked only for severe mental disorder or multiple felonies.
7. Your religion is your own business.
8. Facilities to make large stretches of desert inhabitable will be constructed, and free land will be given to those who agree to settle there.
9. Adulthood will be determined by a battery of psychological tests rather than age.
10. A private citizen may say whatever they wish, wear whatever clothes (if any) they wish, and act in any way that does not harm others. Exposure to nudity or sexual language is not considered harmful.