Restricting access to data based on roles, rights and responsibilities is an integral part of any security policy. It is equally true in the framing of secure hosting.
In this circumstance, access should be clearly separated into roles at different levels. When hosting a web application a separate password and user should be used for database access by the web application. The web application should never have root access to any other domain. In a similar way, real world users should be divided into roles and categories and non-should be granted full root access.
All passwords should be strong and secure - reference the section on strong passwords for further infromation [strong passwords | strong passwords].
Shared Hosting
Dedicated/VPS Hosting