Choose the time-line you want to study. One of the main focuses of demographics is the change in a population that happens with time. For example, the four-stage demographic transition model of pre-industrial, transitional, industrial and post-industrial. (Reference 1)
Study birth and death rates first. These are the basis for population changes. For example, countries that are in transition have birthrates that rise, while the death rate declines. Birth and death rates for industrialized nations differ from those in developing countries.
Study the gross national product. The gross national product (GNP) is the total output of a country that determines its level of industrialized status. The GNP of a country is a clue to a population's behavior; it will tell you where a country is in its population growth process. (Reference 1)
Compare information to the average age in a country. The age of a population will also play a factor in how fast a population is growing. The average age in a country is gathered by a census of the population and this information is used to determine how fast the population will grow.
Study charts. Graphs and charts are a useful tool for visualizing the demographics of a population. The Multimedia Educational Resource for Learning and Online Teaching (Merlot) is an example of an online resource for human demographic charts. (Reference 2)