security Testing approach for an android/ios mobile application

I would like to know what are the thing i have to cover for testing Mobile app for security breaches and that should cover testing on logical side,client side and data security using manual methods of penetration testing

What should be the best approach to test the mobile applications security vulnerabilities. Please share the information and if anybody knows any tools to be use to achieve the same.

I'm looking for android and iOS platform.

Please explain me with a example :)

Eagerly waiting for your response