Apple recommends doing so on an actual device and has a guide on how to do this using QuickTime and iMovie on iOS and OS X: https://developer.apple.com/app-store/app-previews/imovie/Creating-App-Previews-with-iMovie.pdf
Summary:
Capture Screen Recordings with QuickTime Player
Create an App Preview with iMovie
Import Screen Recordings
Next you import the screen recording files that you captured with QuickTime Player into iMovie. In iMovie:
Create an App Preview Project
To start a new app preview project, choose File > New App Preview. A timeline appears where you can add and arrange clips to create your preview.