For almost all cases exceptions in server log or JS errors at browser could help. Additionally you should consider to use:
- browsers debugers
- IDE debuger
If you have cases where nothing works and nothing about errors appeared anywhere - please rise concrete questions and we will check why it's happens. But that could be not only RF responsibility.. Simple example - facelets just ignores wrong attributes names or some erroneous value/method bindings. So nothing thrown and we also spending time sometimes checking such small missprints. But that could not be solved at our level.