1. You need to pick a framework for which you have support within your organization, area that you live or industry vertical that you are working in. I call this stage picking your poison

2. Once you get that then you need to find out how easy it is to integrate with external libraries or extend the framework core classes. The major areas you need to consider are Object Relational Mapping/Database Access (Doctrine/Propel), Model-View-Controller (MVC), Unit Testing (PHPUnit), AJAX, UI Layout, Auto Generation, Performance etc.

3. Once you have picked your poison (1) and made your bed (2), you have to maintain an open mind in that you may need to do somethings different from how the framework designers envisaged them, depending on your project

Start your project and spend the long nights understanding the intricacies of the framework that you have selected.