Make a list of the characteristics your participants should have. These might include age, gender, income, religion, geographical region and marital status. For market research, your characteristics might include buying a particular product or shopping in a particular store. In medical research, a qualitative sample might include people suffering from a particular condition.
Identify and sample every person who meets the sample criteria. This works for studies with sample characteristics that target a very narrow group. If researching customer service in a small business that has only 50 clients, for example, those 50 clients represent your sample.
Identify a location where you can personally select your sample. In some cases, this is the obvious method. For example, if you want to know about customer loyalty to a particular store, find your sample at the store itself. It may be a virtual location---try posting a request on an Internet forum to find people who share a particular specialist interest.
Ask participants to suggest other participants who qualify. For instance, ask participants in an online survey to forward the link to other friends who have the relevant characteristics, such as a particular interest. This is known as network sampling.
Contact people who can suggest participants who fit your profile. In educational research, ask a school principal to nominate students who fulfill your criteria. In health care research, ask a doctor to nominate patients who match your sample characteristics.
Refine your sample by eliminating from the research or results any participants whom you suspect do not meet the requirements or have been dishonest about matching the characteristics.