Questionnaire design is difficult and important to get right as early as possible in a study.
A good questionnaire should be:
Discrimination is the ability of the questionnaire to separate out important differences between the individuals you are studying.
Do not under estimate the time and resource required to develop a valid, reliable and discriminating questionnaire. If there is already a questionnaire that has been developed for your study purpose and validated in a population appropriate to your study then try to use it.
Familiarise yourself with the basic concepts of questionnaire design and analysis at the start of your investigation; texts such as McDowell and Newell (1996) and Streiner and Normal (1995) are available.