Ask clear questions. The questionnaire should only consist of specific questions designed for this category of persons. Consider the social status of the respondents and their education. The only way you will get a specific answer. The question should not be ambiguous. Each question must relate to one subject.
Ask questions that will trigger true answer. It refers to a category of questions on sensitive topics related to personal life and preferences, when people are trying to avoid answering. Mostly in such questions give an answer from personal experience, and according to social norms.
Avoid questions that imply or suggest the answer. For example, start the question with "do you Agree", "do you Own", "do you Know how". Some people, wanting to quickly finish the survey, I agree with you, not thinking about the meaning of the question.
Specify multiple answers. This will simplify the task as easier for people to choose the proposed option than to write the answer.
Combine the compiled questions and answers into a single questionnaire. At the beginning of the questionnaire, place simple questions that will not irritate respondents. The first questions are most important. If the Respondent could not easily reply to them or they cause negative emotions, it can refuse to fill the remainder of the survey. You must first ask General questions, then more specific. This is because if the first Respondent will answer a specific question, then later to the General question on a similar topic will be given a less accurate answer. At the end of the questionnaire you can post questions-detectors. They are rephrasing the questions asked and determine the veracity of the responses received.
Sometimes people are suspicious of filling various questionnaires and surveys, so try gently to get interested in the answers during the conversation, trying to remember the information or quietly outlining the conversation.