Initial questions should be OPEN ENDED. That basically means that they are of a nature that the customer cannot answer them with a "yes" or "no." This forces the customer to reach into his/her mind and surface his own thoughts and feelings. An example would be, "Your organization is quite successful; to what do you attribute this success?"
When you think you may have identified an important need, you follow up with a REFLECTIVE question. Here you are basically mirroring back the customer's thoughts in order to have them expand upon what they said. An example would be. "So you feel state-of-the-art technology and attention to detail is most important for your continuing success?"
When you feel confident you have a need you can address, you use a DIRECTIVE question to focus the customer's attention. An example would be, "If you like our test results, would our solution address your state-of-the-art needs?"