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.
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.