Once you have assigned roles you need to ensure each person clearly understands their position in the development process.
Developers – The first line of defense is clearly the developer. Having great guidelines, detailed information, will be the start of a great process.
Project Manager – The PM should be verifying and validating progress right after development. This helps resolve issues before they even leave the development phase
Tester – A dedicated tester should be in place to test any features or functionality. It is important to have this as an external person, so they are disconnected from the project. This will allow them to view/test the app from the point of view as a end user.
Beta Testers/Client – There should be a short list of beta testers that are involved in testing and feedback. These people will report any issues the encounter, and will be the testers to verify any changes/fixes.