Outline your testing protocol--a description of the steps that anyone on your team can follow to gather feedback from testing. It should include the following sections.
IMPORTANT - You should not explain all the features of your product or lead your users thru a demonstration of its design features. For truly useful feedback, allow your users to interact with your prototypes and discover its features. Try to be an observer, not a tour guide.
Answer any questions that come up as users interact with the prototypes, but keep in mind that asking "what do think will happen?" or "how do you think that might work?" will solicit very useful information about what's going on in the user's mind.
Don't try to sell or pitch your product to your users. You're not trying to convince them that your product is good. Rather, you're hoping to learn from observing and hearing how they feel about your product.
Then, after users have had a chance to explore your prototypes, you can ask about any specific issues that you'd like them to share their feedback on.
For each feature that you're testing, how will you use your prototypes?
What will you ask users to do with your prototypes?
What you will be observing and noting as you watch users interact with your prototypes?
What questions will you ask your users after they've had a chance to interact with and explore your prototypes?