Ways of Collecting Data

Observations

Observation methods have been developed with the objective of 'observing people in their natural setting - as they go about their everyday lives
'Non-participant observation is where the researcher observes behaviour from a distance without interacting with the subject being studied
Participant observation is where the researcher sets out with the aim the aim or 'understanding the world of the subject by putting themselves in their position' Here, the researcher becomes part of the world of the subject, empathising with their position.
Observation methods can overcome some of the criticisms of quantitative research methods (Validity, bias etc.) and can be useful when its subject can't provide information, or can only provide inaccurate information.

(Information By Design. Ltd, NHS, Date unknown: South East Public Health Observatory Lifestyle Survey Toolkit.) http://www.lifestylesurvey.org.uk/observation.html

Interviews

"What is the Interview?
Interviews provide in-depth information about a particular research issue or question. Because the information is not quantifiable (i.e., not amenable to statistical analysis), the interview often is described as a qualitative research method. Whereas quantitative research methods (e.g., the experiment) gather a small amount of information from many subjects, interviews gather a broad range of information from a few subjects.
When we analyze the results from an interview we use the "hermeneutic method." We look at how all the statements made by the interviewee are inter-related. What are the contradictions and consistencies? What is the "big picture" of what the interviewee is trying to say - and how does every individual statement from the interviewee relate to this big picture? The interview is a "holistic" research method: all the bits of data from the interviewee provide you this "big picture" that transcends any one single bit of data.
The information from the interview is not objective data as in quantitative research methods. If the interviewee is an expert on some particular topic or possesses some special skill or experience, his or her responses may be "facts" or "opinions" depending on how you look at it. It really doesn't matter. A good interview is the art and science of exploring the subjective knowledge, opinions, and beliefs of an individual. The knowledge, opinions, and beliefs of that person are a "system." The purpose of the interview is to explore that system and all of its elements".
http://www-usr.rider.edu/~suler/interviews.html#whatis

Questionnaires (also known as Surveys)

"A questionnaire is a research instrument consisting of a series of questions and other prompts for the purpose of gathering information from respondents. Although they are often designed for statistical analysis of the responses, this is not always the case. The questionnaire was invented by Sir Francis Galton.
Questionnaires have advantages over some other types of surveys in that they are cheap, do not require as much effort from the questioner as verbal or telephone surveys, and often have standardized answers that make it simple to compile data. However, such standardized answers may frustrate users. Questionnaires are also sharply limited by the fact that respondents must be able to read the questions and respond to them. Thus, for some demographic groups conducting a survey by questionnaire may not be practical" (Answers Corporation, 2010: Wikipedia-Questionnaire) and http://sophiejgilbert.blogspot.com/2010/03/learning-diary-entry-4.html