You can use information gained from your own monitoring (e.g. sales and marketing data) and feedback you get from direct communication with your customers.
There are two main types – often referred to as primary data and secondary data.
Primary data you collect yourself (or is collected on your behalf) through surveys and group discussions (such as focus groups). Primary Data is gathered to solve a particular problem
Secondary data is previously gathered data. It can include things like published official statistics (such as census data, trade and industry data and demographic statistics) as well as non official material such as internet, newspapers, magazines, reference books, trade directories, trade associations, banks, universities, technical colleges, research institutions and publications from market research organisations.
Both can be useful to you and your business – but which type is best depends on what you want to know. If you want research about how to increase spend per transaction, for example, you might find collecting and analysing primary data most useful.
If you want to break into new markets, you will probably rely much more on secondary data.