Search this forum using the word "questionnaire" for some thoughts.
Read Chapter 2 of Visual Explantions to see John Snow's streetcorner detective work combining statistical data and interviews to figure out a cholera epidemic.
Sometimes a helpful question is of the form: (1) state a fact, and (2) then ask people what they think this might be the case. For example: "250 people on this cruise ship have the Norwalk virus. Wy do you think this happened?" This allows you to see how people reason about a problem in their own words. Maybe this open-ended question will give some insights into how people reason about causes, prevention in their own lives. Such a question might even generate a clue about what happened.
Question-asking in epidemiological research has a long history; you should find the classics in the field and see what was done.
It is often valuable to ask questions that have been asked on other surveys; now you have some baseline comparisons. Also you might ask questions that appeared on the U.S. census; now you can compare census results for the relevant area with the results of your survey. It also a way to detect biases in your sample. Generate external comparisons with your data, both for validation of your survey and to learn more about your respondents compared to the local population. Good questions generate comparisons.
Anything that can be done to reduce the enormous problem (and resulting bias) of nonresponse and refusals is helpful.
-- Edward Tufte
