What's the best way to get user feedback on mobile app pre-launch?

I'm currently working on a mobile app and have design mockups while it is currently under development.

What have you seen as the best way to get user feedback to make sure you are building the right things?

I've been sharing the mockups through InVision and seems to be ok but not the best for quantitative feedback.

Any tools or methods you have used pre-launch to get feedback would be gretly appreciated! Thanks!