If the present number of Earths population is preserved and is reduced only by the means of birth controll, then:
- Birthgiving is licenced. To enhance quality of population , genetically or socially unfit homes will be denied offspring. So that several birth licences can be allowed to families of quality.
- Energy production must be drastically reduced. Electricity is allowed only for the most necessary lighting and communications.
- Food: Hunting is made more efficient. Human diet will include rats and invertebrate animals.
Agriculture moves to small un-mechanized units. All human manure is used as fertilizer.
- Traffic is mostly done with bicycles and rowing boats. Private cars are confiscated. Long-distance travel is done with sparse mass transport. Trees will be planted on most roads.
- Foreign affairs: All mass immigration and most of import-export trade must stop. Cross-border travel is allowed only for small numbers of diplomats and correspondents.
- Business will mostly end . Manufacture is allowed only for well argumented needs. All major manufacturing capacity is state owned. Products will be durable and last for generations.
- Science and schooling: Education will concentrate on practical skills. All competition is rooted out. Technological research is reduced to extreme minimum. But every child will learn how to clean a fish in a way that only the big shiny bones are left over.
http://www.kolumbus.fi/jik/sarastus/penaintr.htm#human 
