When your developer has an initial build to show you, he will be able to share this with you so you can test the app on your iPad or iPhone. While you would assume that testing has taken place on their end, don't.

Open the app and test the current build end-to-end going through every scenario. As you find bugs and problems, write these down using the attached feedback document. Remember to also check any previously open bugs or issues and mark them as open or complete using the same document.

This process will need to be repeated each time an update comes your way. Always re-visit the last feedback version to ensure any previous bugs have been completed, then start with any new bugs you discover.