Listen, don’t tell. Conduct it on their computer. Fix the issues after each test .. iterate like mad, especially when you’re small / trying to figure it out.
Facebook's secret to user testing is keeping data out of the process by doing so you remove the bias and think completely in a UX mindset.
Bite your tongue.
Try to just put the app in front of the user and let them figure it out. What's obvious to you isn't obvious to them.
* The secret to success question is, "How would you...?"
* The secret to success action is literally biting your tongue. Literally.