people respond to your open-ended questions will be directly related to how much they trust you. the things they will wonder about might influence their answers: why are you asking? do you really care about them or the situation you are asking about? how will you use the information—for or against them? will you respond and follow-up with your care and concern?
so the best behavior after asking a good open-ended question is "let silence do the heavy lifting." that, too, takes practice—and patience! 