- Reduce the number of questions to twelve or fewer.
- Clearly state up front the number of questions and the estimated amount of time it will take to complete the survey.
- Replace some of the Likert scale sets of questions with questions suitable for conjoint analysis.
As I've mentioned, the ease of services such as SurveyMonkey causes people to believe that anyone can author a good questionnaire. But the real challenges lie in structuring the survey and formulating the right questions.