To add to what others are saying:
You're looking to quickly design, test, and iterate as quickly as possible. Your goal is to find and fix as many design issues as possible before development. When you've validated all your customers can go through your product, and not only can use it, they understand it, and they love it, you know your design is ready to begin coding. By doing this during the design phase, you'll save 10x what you'd spend fixing design issues during development, and 100x what you'd spend fixing those issues once launched.
1. Make your prototype clickable in InVision using their hotspot tool in Build Mode
2. Develop a screener to ensure your potential users match your target profile, and give you some background on their technical skill level, and relevant skills related to your product. You can use Google Forms for free.
3. Create script outline to include putting customer at ease by letting them know the app is being tested, not her. Ask for honest feedback, you're not going to be hurt. Ask her to "think aloud". Give her tasks to perform and watch what they do, telling you what she's thinking. You're looking for behavior, not opinions. Be prepared to take notes on your script, so you can document your research.
4. Once recruited, connect to potential customers through WebEx, GotoMeeting, or JoinMe to share screens
5. Follow script, asking customer to "say more" and remind to "think aloud". You're not there to tell her she's doing well or not, you're there to listen and learn what works, what's confusing, and what areas of your app need refinement.
And have fun!!!