Explain the factors which determine the level of demand for a good or service

To answer this questions I would reccomend learning the following acronym WISPER CAT

The factors which affect the level of demand are:

Weather

Income

Substitute goods price

Population

Expectations of future prices

Rates - interest

Complimenaty good prices

Advertising

Trends and fashion

If any of the factors above are changed then the level of demand will be affected.